largefiles: restore the original converter class after lfconvert --to-normal

Not sure how much this really matters, but much of the largefiles code that
monkey-patches like this restores things when it finishes.

hgext/largefiles/lfcommands.py

@@ -159,8 +159,13 b' def lfconvert(ui, src, dest, *pats, **op'
             if missing != 0:
                 raise util.Abort(_("all largefiles must be present locally"))
 
+            orig = convcmd.converter
             convcmd.converter = converter
-            convcmd.convert(ui, src, dest)
+
+            try:
+                convcmd.convert(ui, src, dest)
+            finally:
+                convcmd.converter = orig
         success = True
     finally:
         if tolfile: