largefiles: remove a mutable default argument

Mutable default arguments are know to the state of California to cause bugs.

hgext/largefiles/overrides.py

@@ -617,7 +617,7 b' def overridecopy(orig, ui, repo, pats, o'
         wlock = repo.wlock()
 
         manifest = repo[None].manifest()
-        def overridematch(ctx, pats=[], opts={}, globbed=False,
+        def overridematch(ctx, pats=(), opts={}, globbed=False,
                 default='relpath', badfn=None):
             newpats = []
             # The patterns were previously mangled to add the standin