Gtk theme: emit currentFontChanged() in font dialog helper

There is no signal for it in gtk font selection. We should emit this
signal just before accept() was emitted.

Change-Id: Ie31d96b789436607b134c84dd77a4b9be9e9a550
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>

src/plugins/platformthemes/gtk2/qgtk2dialoghelpers.cpp

@@ -587,6 +587,7 @@ QFont QGtk2FontDialogHelper::currentFont() const
 
 void QGtk2FontDialogHelper::onAccepted()
 {
+    emit currentFontChanged(currentFont());
     emit accept();
     emit fontSelected(currentFont());
 }