Fix bugtracker #251: title block template with slash in name fails silently

Saving a new user title block template (right-click "Cartouches
utilisateur" > "Nouveau modèle" > "Enregistrer sous") with a name
containing a slash (or other filesystem-reserved character) silently
did nothing, with no error shown. The entered name is turned directly
into a filename (TitleBlockTemplatesFilesCollection::toFileName()), so
e.g. "foo/bar" becomes a path "foo/bar.titleblock" -- since "foo/"
essentially never exists as a directory, the underlying file write
fails, but that failure was never surfaced:

- TitleBlockTemplateLocation::isValid() only checked for an empty
  name, so an invalid name still counted as "valid" and got passed
  through to save.
- QETTitleBlockTemplateEditor::saveAs(const TitleBlockTemplateLocation&)
  discarded the bool result of setTemplateXmlDescription() and
  unconditionally returned true, marking the undo stack clean as if
  the save had actually succeeded.

Fix:
- isValid() now also rejects names containing \ / : * ? " < > |,
  matching the character set that's actually unsafe once the name
  becomes a filename.
- saveAs() (the no-arg entry point that asks the user for a location)
  now shows a clear error dialog when the entered name is rejected,
  distinguishing "user cancelled" (location.name() empty) from
  "name was invalid" (non-empty but rejected by isValid()).
- saveAs(location) now checks setTemplateXmlDescription()'s return
  value and shows an error dialog instead of reporting false success
  on any future/other write failure, not just this one.

Verified: clean rebuild, only the intended files recompiled and
linked successfully. Live-tested under Xvfb: creating a new template
and using "Enregistrer sous" with the name "foo/bar" now shows
"Le nom « foo/bar » n'est pas valide : il ne doit pas contenir les
caractères suivants : \ / : * ? " < > |" instead of silently doing
nothing; reopening the save-as dialog afterward showed the name field
correctly empty (nothing was partially written). Saving again with a
valid name ("mytemplate_valid") completed with no error dialog, and
the resulting mytemplate_valid.titleblock file was confirmed present
on disk in the user's title-block collection directory.

sources/titleblock/qettemplateeditor.cpp

@@ -776,7 +776,20 @@ bool QETTitleBlockTemplateEditor::saveAs(const TitleBlockTemplateLocation &locat
 	elmt.setAttribute("name", location.name());
 	doc.appendChild(elmt);
 
-	collection -> setTemplateXmlDescription(location.name(), elmt);
+	if (!collection -> setTemplateXmlDescription(location.name(), elmt)) {
+			// Report the failure instead of marking the template "saved"
+			// regardless (bugtracker #251) -- this return value used to
+			// be discarded here.
+		QET::QetMessageBox::critical(
+			this,
+			tr("Erreur", "message box title"),
+			tr(
+				"Impossible d'enregistrer le modèle « %1 ».",
+				"message box content - %1 is a title block template name"
+			).arg(location.name())
+		);
+		return(false);
+	}
 
 	opened_from_file_ = false;
 	location_ = location;
@@ -880,6 +893,21 @@ bool QETTitleBlockTemplateEditor::saveAs()
 	if (location.isValid()) {
 		return(saveAs(location));
 	}
+	if (!location.name().isEmpty()) {
+			// The name was rejected (e.g. contains a path separator or
+			// other filesystem-reserved character) rather than the user
+			// cancelling the dialog -- say so instead of silently doing
+			// nothing (bugtracker #251).
+		QET::QetMessageBox::critical(
+			this,
+			tr("Erreur", "message box title"),
+			tr(
+				"Le nom « %1 » n'est pas valide : il ne doit pas contenir "
+				"les caractères suivants : \\ / : * ? \" < > |",
+				"message box content - %1 is the rejected template name"
+			).arg(location.name())
+		);
+	}
 	return(false);
 }
 

sources/titleblock/templatelocation.cpp

@@ -92,7 +92,13 @@ void TitleBlockTemplateLocation::setName(const QString &name) {
 */
 bool TitleBlockTemplateLocation::isValid() const
 {
-	return(!name_.isEmpty());
+	// The name becomes (part of) a filename on disk (see
+	// TitleBlockTemplatesFilesCollection::toFileName()). A name containing
+	// a path separator or another filesystem-reserved character silently
+	// fails to save instead of erroring, because it turns into an
+	// unintended subpath rather than a plain filename (bugtracker #251).
+	static const QRegularExpression invalid_chars_re(QStringLiteral("[\\\\/:*?\"<>|]"));
+	return(!name_.isEmpty() && !name_.contains(invalid_chars_re));
 }
 
 /**