VCS: Make submit editor closing independent from current editor

The VCS plugins keep a reference to the submit editor, so it can
explicitly be closed, instead of relying on the correct currentEditor in
the editor manager.

Change-Id: I14aab63447f790f2065a8d8dc6b50aeacbd1e941
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/perforce/perforceplugin.cpp

@@ -1329,7 +1329,7 @@ void PerforcePlugin::describe(const QString & source, const QString &n)
 void PerforcePlugin::submitCurrentLog()
 {
     m_submitActionTriggered = true;
-    EditorManager::closeEditor(EditorManager::currentEditor());
+    EditorManager::closeEditor(submitEditor());
 }
 
 void PerforcePlugin::cleanCommitMessageFile()