Git: Update file model after unsuccessful commit

The commit operation itself [un]stages files before actually committing.
The model has to be refreshed after that.

Change-Id: I4b765005640b62812687d4f003d94af3717c379e
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/git/gitplugin.cpp

@@ -1078,6 +1078,7 @@ bool GitPlugin::submitEditorAboutToClose()
 
         if (!m_gitClient->addAndCommit(m_submitRepository, editor->panelData(), commitType,
                                        amendSHA1, m_commitMessageFileName, model)) {
+            editor->updateFileModel();
             return false;
         }
     }