pack-objects: Fix segfault when object count is less than thread count

When partitioning the work amongst threads, dividing the number of
objects by the number of threads may return 0 when there are less
objects than threads; this will cause the subsequent code to segfault
when accessing list[sub_size-1].  Fix this by ensuring that sub_size
is not zero if there is at least one object to process.

Signed-off-by: Sergey Vlasov <redacted>
---
 builtin-pack-objects.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/builtin-pack-objects.c b/builtin-pack-objects.c
index ec10238..cdf8aae 100644
--- a/builtin-pack-objects.c
+++ b/builtin-pack-objects.c

@@ -1665,6 +1665,9 @@ static void ll_find_deltas(struct object_entry **list, unsigned list_size,
 	for (i = 0; i < delta_search_threads; i++) {
 		unsigned sub_size = list_size / (delta_search_threads - i);
 
+		if (sub_size == 0 && list_size >= 1)
+			sub_size = 1;
+
 		p[i].window = window;
 		p[i].depth = depth;
 		p[i].processed = processed;

-- 
1.5.4.rc4.14.gd50a3