Merge pull request #6029 from arroz/fix_6028

#6028: Check if `threadstate->error_t.message` is not `git_buf__initbuf` before freeing.

src/threadstate.c

@@ -36,6 +36,7 @@ static void threadstate_dispose(git_threadstate *threadstate)
 	if (!threadstate)
 		return;
 
+    if (threadstate->error_t.message != git_buf__initbuf)
         git__free(threadstate->error_t.message);
 	threadstate->error_t.message = NULL;
 }