Merge branch 'js/check-null-from-read-object-file'

The code paths that call repo_read_object_file() have been
tightened to react to errors.

* js/check-null-from-read-object-file:
  Always check the return value of `repo_read_object_file()`

combine-diff.c

@@ -337,6 +337,8 @@ static char *grab_blob(struct repository *r,
 		free_filespec(df);
 	} else {
 		blob = repo_read_object_file(r, oid, &type, size);
+		if (!blob)
+			die(_("unable to read %s"), oid_to_hex(oid));
 		if (type != OBJ_BLOB)
 			die("object '%s' is not a blob!", oid_to_hex(oid));
 	}