hg: update newly added listdir function of vfs in clone

This change invokes os.listdir() via newly added vfs function in clone.

mercurial/hg.py

@@ -316,7 +316,7 b' def clone(ui, peeropts, source, dest=Non'
     if destvfs.lexists():
         if not destvfs.isdir():
             raise util.Abort(_("destination '%s' already exists") % dest)
-        elif os.listdir(dest):
+        elif destvfs.listdir():
             raise util.Abort(_("destination '%s' is not empty") % dest)
 
     srclock = destlock = cleandir = None