ui-snapshot.c: Fill argv[0] with dummy.

parse_archive_args does not pass PARSE_OPT_KEEP_ARGV0 to parse_args,
which means the first argument will be discarded, as though it were a
function being called from the command-line. Thus, we fill argv[0] with
a dummy argument to prevent this from happening.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

ui-snapshot.c

@@ -14,6 +14,7 @@
 static int write_archive_type(const char *format, const char *hex, const char *prefix)
 {
 	struct argv_array argv = ARGV_ARRAY_INIT;
+	argv_array_push(&argv, "snapshot");
 	argv_array_push(&argv, format);
 	if (prefix) {
 		argv_array_push(&argv, "--prefix");