merge-ort: fix missing early return

One of the conversions in f19b9165 (merge-ort: convert more error()
cases to path_msg(), 2024-06-19) accidentally lost the early return.

Restore it.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

merge-ort.c

@@ -3618,6 +3618,7 @@ static int read_oid_strbuf(struct merge_options *opt,
 		path_msg(opt, ERROR_OBJECT_NOT_A_BLOB, 0,
 			 path, NULL, NULL, NULL,
 			 _("error: object %s is not a blob"), oid_to_hex(oid));
+		return -1;
 	}
 	strbuf_attach(dst, buf, size, size + 1);
 	return 0;