merge-blobs.c: fix a memleak

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

merge-blobs.c

@@ -14,8 +14,10 @@ static int fill_mmfile_blob(mmfile_t *f, struct blob *obj)
 	buf = read_sha1_file(obj->object.sha1, &type, &size);
 	if (!buf)
 		return -1;
-	if (type != OBJ_BLOB)
+	if (type != OBJ_BLOB) {
+		free(buf);
 		return -1;
+	}
 	f->ptr = buf;
 	f->size = size;
 	return 0;