Fix Console output on save error (openscad#5637)

"File/Save As..." to a read-only directory can cause invalid characters
to be written to the Console.

Author: cjmayo

src/gui/TabManager.cc

@@ -618,8 +618,8 @@ bool TabManager::shouldClose()
 
 void TabManager::saveError(const QIODevice& file, const std::string& msg, const QString& filepath)
 {
-  const char *fileName = filepath.toLocal8Bit().constData();
-  LOG("%1$s %2$s (%3$s)", msg.c_str(), fileName, file.errorString().toLocal8Bit().constData());
+  const std::string fileName = filepath.toStdString();
+  LOG("%1$s %2$s (%3$s)", msg.c_str(), fileName, file.errorString().toStdString());
 
   const std::string dialogFormatStr = msg + "\n\"%1\"\n(%2)";
   const QString dialogFormat(dialogFormatStr.c_str());