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/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);