Make the font restoration counters safe against nested project loads

DialogWaiting pumps the event loop while the folios of a project are
built, so a second openAndAddProject() can run to completion nested
inside the first one (drop on another editor window, queued open) and
the plain reset/read counters would then report the wrong numbers.

Replace them with a RAII counting window (FontRestorationScope): the
constructor keeps the enclosing counts aside, the destructor restores
them. The nesting is strictly LIFO - the nested load completes inside
the pump of the outer one - so each load reports exactly its own
numbers, and the early-return paths of openAndAddProject() restore the
outer window automatically.

Suggested by ispyisail in the review of the reporting change.

sources/qetdiagrameditor.cpp

@@ -1171,8 +1171,10 @@ bool QETDiagramEditor::openAndAddProject(
 
 		//Per-project window for the font counters reported below; the folios
 		//(and with them the stored font descriptions) are built between here
-		//and the end of addProject().
-	QETUtils::resetFontRestorationCounters();
+		//and the end of addProject(). RAII, because DialogWaiting pumps the
+		//event loop during the load: a nested openAndAddProject() gets its
+		//own window and this one resumes unharmed.
+	QETUtils::FontRestorationScope font_scope;
 
 	QETProject *project = new QETProject(filepath);
 	if (project -> state() != QETProject::Ok)
@@ -1203,8 +1205,8 @@ bool QETDiagramEditor::openAndAddProject(
 		//Report font descriptions which could not be read as-is (written by
 		//an incompatible Qt version or corrupted), so the user learns about
 		//it from somewhere else than the console. See issue #553.
-	const int salvaged_fonts = QETUtils::salvagedFontCount();
-	const int unreadable_fonts = QETUtils::unreadableFontCount();
+	const int salvaged_fonts = font_scope.salvaged();
+	const int unreadable_fonts = font_scope.unreadable();
 	if (salvaged_fonts || unreadable_fonts)
 	{
 		qInfo().nospace() << "Project font descriptions: "

sources/utils/qetutils.cpp

@@ -304,33 +304,42 @@ bool QETUtils::fontFromString(QFont &font, const QString &description)
 }
 
 /**
- * @brief QETUtils::resetFontRestorationCounters
- * Reset the counters incremented by fontFromString(), to be called before
- * loading a project so the numbers reported afterwards are per-project.
+ * @brief QETUtils::FontRestorationScope::FontRestorationScope
+ * Open a fresh counting window: the enclosing window's counts are kept
+ * aside and restored by the destructor, so a project load nested inside
+ * another one (through the event loop) reports its own numbers only.
  */
-void QETUtils::resetFontRestorationCounters()
+QETUtils::FontRestorationScope::FontRestorationScope() :
+	m_outer_salvaged(salvaged_font_count),
+	m_outer_unreadable(unreadable_font_count)
 {
 	salvaged_font_count = 0;
 	unreadable_font_count = 0;
 }
 
+QETUtils::FontRestorationScope::~FontRestorationScope()
+{
+	salvaged_font_count = m_outer_salvaged;
+	unreadable_font_count = m_outer_unreadable;
+}
+
 /**
- * @brief QETUtils::salvagedFontCount
+ * @brief QETUtils::FontRestorationScope::salvaged
  * @return How many font descriptions fontFromString() restored from a
- * foreign or corrupt format since the counters were last reset. Such
- * descriptions are rewritten in the stable format on the next save.
+ * foreign or corrupt format since this window was opened. Such descriptions
+ * are rewritten in the stable format on the next save.
  */
-int QETUtils::salvagedFontCount()
+int QETUtils::FontRestorationScope::salvaged() const
 {
 	return salvaged_font_count;
 }
 
 /**
- * @brief QETUtils::unreadableFontCount
+ * @brief QETUtils::FontRestorationScope::unreadable
  * @return How many font descriptions fontFromString() could not restore at
- * all since the counters were last reset (the caller's default font applies).
+ * all since this window was opened (the caller's default font applies).
  */
-int QETUtils::unreadableFontCount()
+int QETUtils::FontRestorationScope::unreadable() const
 {
 	return unreadable_font_count;
 }

sources/utils/qetutils.h

@@ -34,9 +34,29 @@ namespace QETUtils
     void pixelSizedFont (QFont &font);
     QString fontToString (const QFont &font);
     bool fontFromString (QFont &font, const QString &description);
-    void resetFontRestorationCounters ();
-    int salvagedFontCount ();
-    int unreadableFontCount ();
+
+	/**
+		RAII counting window for the font descriptions fontFromString()
+		salvages or fails to read: construction opens a fresh window, the
+		destructor restores the enclosing one. Windows nest strictly LIFO,
+		which covers project loads re-entered through the event loop
+		(DialogWaiting pumps it while the folios are built).
+	*/
+	class FontRestorationScope
+	{
+		public:
+			FontRestorationScope();
+			~FontRestorationScope();
+			FontRestorationScope(const FontRestorationScope &) = delete;
+			FontRestorationScope &operator=(const FontRestorationScope &) = delete;
+
+			int salvaged() const;
+			int unreadable() const;
+
+		private:
+			int m_outer_salvaged;
+			int m_outer_unreadable;
+	};
 
 	bool sortBeginIntString(const QString &str_a, const QString &str_b);