GUI: Restore settings if GUI cannot be rendered

PR#921 changes the behavior of the client that if the GUI fails to be
rendered the previously applied settings in the misc category are
restored. Error messages were altered according to the changes.

Bug: #9717 GUI: Indirectly changing 'GUI Language' can produce
                inconsistent behaviour when changing some options.

gui/ThemeEngine.cpp

@@ -722,7 +722,9 @@ bool ThemeEngine::addFont(TextData textId, const Common::String &file, const Com
 #ifdef USE_TRANSLATION
 			TransMan.setLanguage("C");
 #endif
-			warning("Failed to load localized font '%s'. Using non-localized font and default GUI language instead", localized.c_str());
+			warning("Failed to load localized font '%s'.", localized.c_str());
+
+			return false;
 		}
 	}