mq: take wlock when 'qqueue' is doing write operations

Apparently when this command was added, the locking was forgotten. No code
changes beside the indentation from the locking context.

hgext/mq.py

@@ -3354,6 +3354,7 def qqueue(ui, repo, name=None, **opts):
         raise error.Abort(
                 _('invalid queue name, may not contain the characters ":\\/."'))
 
+    with repo.wlock():
     existing = _getqueues()
 
     if opts.get('create'):