revlog: fix a typo closing the wrong file

Caught by pytype as possibly being None, but the file is closed in the previous
conditional.

Differential Revision: https://phab.mercurial-scm.org/D10874

mercurial/revlog.py

@@ -2243,7 +2243,7 b' class revlog(object):'
                 if dfh is not None:
                     dfh.close()
                 if sdfh is not None:
-                    dfh.close()
+                    sdfh.close()
                 # closing the index file last to avoid exposing referent to
                 # potential unflushed data content.
                 if ifh is not None: