[PATCH 2/3] create_snapshot(): exit early if the file was empty

[Michael Haggerty <mhagger@alum.mit.edu>]

If the `packed_refs` files is entirely empty (i.e., not even a header
line), then `load_contents()` returns 1 even though `snapshot->buf`
and `snapshot->eof` both end up set to NULL. In that case, the
subsequent processing that `create_snapshot()` does is unnecessary,
and also involves computing `NULL - NULL` and `NULL + 0`, which are
probably safe in real life but are technically undefined in C.

Sidestep both issues by exiting early if `snapshot->buf` is NULL.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
---
 refs/packed-backend.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index f20f05b4df..36796d65f0 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -613,7 +613,7 @@ static struct snapshot *create_snapshot(struct packed_ref_store *refs)
 	acquire_snapshot(snapshot);
 	snapshot->peeled = PEELED_NONE;
 
-	if (!load_contents(snapshot))
+	if (!load_contents(snapshot) || !snapshot->buf)
 		return snapshot;
 
 	/* If the file has a header line, process it: */
-- 
2.14.2