Merge branch 'js/merge-ort-in-read-only-repo' into maint-2.38

In read-only repositories, "git merge-tree" tried to come up with a
merge result tree object, which it failed (which is not wrong) and
led to a segfault (which is bad), which has been corrected.

* js/merge-ort-in-read-only-repo:
  merge-ort: return early when failing to write a blob
  merge-ort: fix segmentation fault in read-only repositories