largefiles: replace splitstandin() by isstandin() to omit str creation

If splitstandin()-ed str itself isn't used, isstandin() should be
used instead of it, to omit meaningless str creation.

hgext/largefiles/overrides.py

@@ -351,7 +351,7 b' def overridelog(orig, ui, repo, *pats, *'
             pats.update(fixpats(f, tostandin) for f in p)
         else:
             def tostandin(f):
-                if lfutil.splitstandin(f):
+                if lfutil.isstandin(f):
                     return f
                 return lfutil.standin(f)
             pats.update(fixpats(f, tostandin) for f in p)