large-files: larger "changing_parents" context in mergeupdate override

This since we are updating the lfdirstate early, it seems reasonable to include
the full function in that scope.

hgext/largefiles/overrides.py

@@ -1769,7 +1769,7 b' def mergeupdate(orig, repo, node, branch'
     matcher = kwargs.get('matcher', None)
     # note if this is a partial update
     partial = matcher and not matcher.always()
-    with repo.wlock():
+    with repo.wlock(), repo.dirstate.changing_parents(repo):
         # branch |       |         |
         #  merge | force | partial | action
         # -------+-------+---------+--------------
@@ -1837,8 +1837,6 b' def mergeupdate(orig, repo, node, branch'
             raise error.ProgrammingError(
                 b'largefiles is not compatible with in-memory merge'
             )
-        with repo.dirstate.changing_parents(repo):
-            lfdirstate = lfutil.openlfdirstate(repo.ui, repo)
             result = orig(repo, node, branchmerge, force, *args, **kwargs)
 
             newstandins = lfutil.getstandinsstate(repo)