t5316: check behavior of pack-objects --depth=0

We'd expect this to cleanly produce no deltas at all (as opposed to
getting confused by an out-of-bounds value), and it does.

Note we have to adjust our max_chain test helper, which expected to find
at least one delta.

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

t/t5316-pack-delta-depth.sh

@@ -69,6 +69,7 @@ test_expect_success 'create series of packs' '
 max_chain() {
 	git index-pack --verify-stat-only "$1" >output &&
 	perl -lne '
+	  BEGIN { $len = 0 }
 	  /chain length = (\d+)/ and $len = $1;
 	  END { print $len }
 	' output
@@ -94,4 +95,11 @@ test_expect_success '--depth limits depth' '
 	test_cmp expect actual
 '
 
+test_expect_success '--depth=0 disables deltas' '
+	pack=$(git pack-objects --all --depth=0 </dev/null pack) &&
+	echo 0 >expect &&
+	max_chain pack-$pack.pack >actual &&
+	test_cmp expect actual
+'
+
 test_done