Fix crash from bad toolbox reference during shutdown

src/QmlControls/AppMessages.cc

@@ -92,8 +92,7 @@ void AppLogModel::threadsafeLog(const QString message)
     insertRows(line, 1);
     setData(index(line), message, Qt::DisplayRole);
 
-    if (qgcApp()->logOutput()) {
-        if (_logFile.fileName().isEmpty()) {
+    if (_logFile.fileName().isEmpty() && qgcApp()->logOutput()) {
         QGCToolbox* toolbox = qgcApp()->toolbox();
         // Be careful of toolbox not being open yet
         if (toolbox) {
@@ -112,5 +111,4 @@ void AppLogModel::threadsafeLog(const QString message)
         QTextStream out(&_logFile);
         out << message << "\n";
     }
-    }
 }