Base: fix crash in PyException::ReportException()

src/Base/Interpreter.cpp

@@ -126,6 +126,7 @@ void PyException::ReportException () const
     if (!_isReported) {
         _isReported = true;
         // set sys.last_vars to make post-mortem debugging work
+        PyGILStateLocker locker;
         PySys_SetObject("last_traceback", PP_last_traceback);
         Base::Console().DeveloperError("pyException","%s%s: %s\n",
             _stackTrace.c_str(), _errorType.c_str(), what());