convert: make hg sink cleanup safer

hgext/convert/hg.py

@@ -61,7 +61,9 class mercurial_sink(converter_sink):
 
     def after(self):
         self.ui.debug('run hg sink post-conversion action\n')
+        if self.lock:
         self.lock.release()
+        if self.wlock:
         self.wlock.release()
 
     def revmapfile(self):