sha1_file.c: do not die failing to malloc in unpack_compressed_entry

Fewer die() gives better control to the caller, provided that the
caller _can_ handle it. And in unpack_compressed_entry() case, it can,
because unpack_compressed_entry() already returns NULL if it fails to
inflate data.

A side effect from this is fsck continues to run when very large blobs
are present (and do not fit in memory).
Noticed-by: NDale R. Worley <worley@alum.mit.edu>
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

sha1_file.c

@@ -1923,7 +1923,9 @@ static void *unpack_compressed_entry(struct packed_git *p,
 	git_zstream stream;
 	unsigned char *buffer, *in;
 
-	buffer = xmallocz(size);
+	buffer = xmallocz_gently(size);
+	if (!buffer)
+		return NULL;
 	memset(&stream, 0, sizeof(stream));
 	stream.next_out = buffer;
 	stream.avail_out = size + 1;

t/t1050-large.sh

@@ -163,4 +163,10 @@ test_expect_success 'zip achiving, deflate' '
 	git archive --format=zip HEAD >/dev/null
 '
 
+test_expect_success 'fsck' '
+	test_must_fail git fsck 2>err &&
+	n=$(grep "error: attempting to allocate .* over limit" err | wc -l) &&
+	test "$n" -gt 1
+'
+
 test_done