Merge branch 'jk/has-uncommitted-changes-fix'

"git pull --rebase" on a corrupt HEAD caused a segfault.  In
general we substitute an empty tree object when running the in-core
equivalent of the diff-index command, and the codepath has been
corrected to do so as well to fix this issue.

* jk/has-uncommitted-changes-fix:
has_uncommitted_changes(): fall back to empty tree

diff --cc diff-lib.c
index a9f38eb5a3e0e17d111301b581d06876ce5fd510,7eea70e8139672749733c812db3e9848055f53c5..732f684a49c54cdbc3b9708e91c064b7845d7716
--- 1/diff-lib.c
--- 2/diff-lib.c
+++ b/diff-lib.c
@@@ -518,8 -512,10 +518,11 @@@ static int diff_cache(struct rev_info *
  int run_diff_index(struct rev_info *revs, int cached)
  {
        struct object_array_entry *ent;
 +      uint64_t start = getnanotime();
  
+       if (revs->pending.nr != 1)
+               BUG("run_diff_index must be passed exactly one tree");
+ 
        ent = revs->pending.objects;
        if (diff_cache(revs, &ent->item->oid, ent->name, cached))
                exit(128);

diff --cc wt-status.c
Simple merge