Git: Fix crash when fetch is done while context menu is active

Blind shot.

Task-number: QTCREATORBUG-29266
Change-Id: Ie9e8be9e6ead7a3c49cdde7c3b80b4735f7b19af
Reviewed-by: hjk <hjk@qt.io>

src/plugins/git/branchview.h

@@ -75,6 +75,7 @@ private:
     BranchFilterModel *m_filterModel = nullptr;
     Utils::FilePath m_repository;
     bool m_blockRefresh = false;
+    bool m_postponedRefresh = false;
 };
 
 class BranchViewFactory : public Core::INavigationWidgetFactory