pack-objects: check return value from read_sha1_file()

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-pack-objects.c

@@ -1356,6 +1356,9 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 	/* Load data if not already done */
 	if (!trg->data) {
 		trg->data = read_sha1_file(trg_entry->idx.sha1, &type, &sz);
+		if (!trg->data)
+			die("object %s cannot be read",
+			    sha1_to_hex(trg_entry->idx.sha1));
 		if (sz != trg_size)
 			die("object %s inconsistent object length (%lu vs %lu)",
 			    sha1_to_hex(trg_entry->idx.sha1), sz, trg_size);
@@ -1363,6 +1366,9 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 	}
 	if (!src->data) {
 		src->data = read_sha1_file(src_entry->idx.sha1, &type, &sz);
+		if (!src->data)
+			die("object %s cannot be read",
+			    sha1_to_hex(src_entry->idx.sha1));
 		if (sz != src_size)
 			die("object %s inconsistent object length (%lu vs %lu)",
 			    sha1_to_hex(src_entry->idx.sha1), sz, src_size);