Disable debug logger on close

The logger can be closed from the external thread (openshot-qt), while
same logger instance is still in use in libopenshot.

This change prevents crash on attempts to use debug logger if it was
closed.

Co-authored-by: Frank Dana <ferdnyc@users.noreply.github.com>

src/ZmqLogger.cpp

@@ -160,6 +160,9 @@ void ZmqLogger::Path(string new_path)
 
 void ZmqLogger::Close()
 {
+	// Disable logger as it no longer needed
+	enabled = false;
+
 	// Close file (if already open)
 	if (log_file.is_open())
 		log_file.close();