Set commit date on snapshot contents

The testsuite revealed that cgit snapshots don't set any useful timestamp on
the files contained in the snapshot.

Cherry-picked-from: 2ff33a8a04
Signed-off-by: Lars Hjemli <hjemli@gmail.com>

ui-snapshot.c

@@ -99,6 +99,7 @@ void cgit_print_snapshot(struct cacheitem *item, const char *head,
 		memset(&args,0,sizeof(args));
 		args.base = fmt("%s/", prefix);
 		args.tree = commit->tree;
+		args.time = commit->date;
 		cgit_print_snapshot_start(sat->mimetype, filename, item);
 		(*sat->write_func)(&args);
 		return;