fetch: release pack files before garbage-collecting

Before auto-gc'ing, we need to make sure that the pack files are
released in case they need to be repacked and garbage-collected.

This fixes https://github.com/git-for-windows/git/issues/500

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/fetch.c

@@ -1221,6 +1221,8 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 	list.strdup_strings = 1;
 	string_list_clear(&list, 0);
 
+	close_all_packs();
+
 	argv_array_pushl(&argv_gc_auto, "gc", "--auto", NULL);
 	if (verbosity < 0)
 		argv_array_push(&argv_gc_auto, "--quiet");

t/t5510-fetch.sh

@@ -708,4 +708,17 @@ test_expect_success 'fetching a one-level ref works' '
 	)
 '
 
+test_expect_success 'fetching with auto-gc does not lock up' '
+	write_script askyesno <<-\EOF &&
+	echo "$*" &&
+	false
+	EOF
+	git clone "file://$D" auto-gc &&
+	test_commit test2 &&
+	cd auto-gc &&
+	git config gc.autoPackLimit 1 &&
+	GIT_ASK_YESNO="$D/askyesno" git fetch >fetch.out 2>&1 &&
+	! grep "Should I try again" fetch.out
+'
+
 test_done