t5500: add test for fetching with an unknown 'shallow'

When the client sends a 'shallow' line for an object that the server does
not have, the server should just ignore it and let the client keep that
unknown shallow boundary.

Signed-off-by: Michael Heemskerk <mheemskerk@atlassian.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5500-fetch-pack.sh

@@ -373,6 +373,20 @@ test_expect_success 'clone shallow with packed refs' '
 	test_cmp count8.expected count8.actual
 '
 
+test_expect_success 'fetch in shallow repo unreachable shallow objects' '
+	(
+		git clone --bare --branch B --single-branch "file://$(pwd)/." no-reflog &&
+		git clone --depth 1 "file://$(pwd)/no-reflog" shallow9 &&
+		cd no-reflog &&
+		git tag -d TAGB1 TAGB2 &&
+		git update-ref refs/heads/B B~~ &&
+		git gc --prune=now &&
+		cd ../shallow9 &&
+		git fetch origin &&
+		git fsck --no-dangling
+	)
+'
+
 test_expect_success 'setup tests for the --stdin parameter' '
 	for head in C D E F
 	do