RefactoringFile: Use editor's cursor, if possible.

This fixes 'undo' with quick fixes not preserving the original cursor
position.

Change-Id: If6475a5afab3e806ea713c769f730c6ffd773298
Reviewed-by: hjk <qthjk@ovi.com>
Reviewed-by: Leandro T. C. Melo <leandro.melo@nokia.com>

src/plugins/texteditor/refactoringchanges.cpp

@@ -339,7 +339,7 @@ void RefactoringFile::apply()
             return;
 
         {
-            QTextCursor c(doc);
+            QTextCursor c = cursor();
             c.beginEditBlock();
 
             // build indent selections now, applying the changeset will change locations