Compilation fix for wxGTK3 after PangoFontFace fix.

Bracket the changes of 54e653d044 with a glib
version check: g_type_ensure() is only available in 2.34+.

See #16820.

src/gtk/fontdlg.cpp

@@ -78,7 +78,9 @@ bool wxFontDialog::DoCreate(wxWindow *parent)
         gtk_parent = GTK_WINDOW(parent->m_widget);
 
 #if GTK_CHECK_VERSION(3,2,0)
+#if GLIB_CHECK_VERSION(2, 34, 0)
     g_type_ensure(PANGO_TYPE_FONT_FACE);
+#endif
     if (gtk_check_version(3,2,0) == NULL)
         m_widget = gtk_font_chooser_dialog_new(wxGTK_CONV(message), gtk_parent);
     else