largefiles: don't crash on 'local renamed directory' actions

a12798938721 introduced splitstandin on all action filenames. It would however
crash on 'd' actions where the filename is None.

Fix that and add test coverage for that case.

hgext/largefiles/overrides.py

@@ -380,7 +380,7 b' def overridemanifestmerge(origfn, repo, '
     for action in actions:
         f, m, args, msg = action
 
-        splitstandin = lfutil.splitstandin(f)
+        splitstandin = f and lfutil.splitstandin(f)
         if (m == "g" and splitstandin is not None and
             splitstandin in p1 and splitstandin not in removes):
             # Case 1: normal file in the working copy, largefile in

tests/test-largefiles.t

@@ -2192,6 +2192,39 b' check messages when there are files to u'
 
   $ cd ..
 
+merge action 'd' for 'local renamed directory to d2/g' which has no filename
+
+  $ hg init merge-action
+  $ cd merge-action
+  $ touch l
+  $ hg add --large l
+  $ mkdir d1
+  $ touch d1/f
+  $ hg ci -Aqm0
+  Invoking status precommit hook
+  A d1/f
+  A l
+  $ echo > d1/f
+  $ touch d1/g
+  $ hg ci -Aqm1
+  Invoking status precommit hook
+  M d1/f
+  A d1/g
+  $ hg up -qr0
+  $ hg mv d1 d2
+  moving d1/f to d2/f (glob)
+  $ hg ci -qm2
+  Invoking status precommit hook
+  A d2/f
+  R d1/f
+  $ hg merge
+  merging d2/f and d1/f to d2/f
+  1 files updated, 1 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+  getting changed largefiles
+  0 largefiles updated, 0 removed
+  $ cd ..
+
 Check whether "largefiles" feature is supported only in repositories
 enabling largefiles extension.