index-pack: skip collision check when not in repository

You can run "git index-pack path/to/foo.pack" outside of a
repository to generate an index file, or just to verify the
contents. There's no point in doing a collision check, since
we obviously do not have any objects to collide with.

The current code will blindly look in .git/objects based on
the result of setup_git_env(). That effectively gives us the
right answer (since we won't find any objects), but it's a
waste of time, and it conflicts with our desire to
eventually get rid of the "fallback to .git" behavior of
setup_git_env().

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/index-pack.c

@@ -787,13 +787,15 @@ static void sha1_object(const void *data, struct object_entry *obj_entry,
 			const unsigned char *sha1)
 {
 	void *new_data = NULL;
-	int collision_test_needed;
+	int collision_test_needed = 0;
 
 	assert(data || obj_entry);
 
-	read_lock();
-	collision_test_needed = has_sha1_file_with_flags(sha1, HAS_SHA1_QUICK);
-	read_unlock();
+	if (startup_info->have_repository) {
+		read_lock();
+		collision_test_needed = has_sha1_file_with_flags(sha1, HAS_SHA1_QUICK);
+		read_unlock();
+	}
 
 	if (collision_test_needed && !data) {
 		read_lock();