parseopt: use boolean type for a simple flag

Suggested-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: D. Ben Knoble <ben.knoble+github@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: benknoble

parse-options.c

@@ -208,7 +208,7 @@ static enum parse_opt_result do_get_value(struct parse_opt_ctx_t *p,
 	case OPTION_FILENAME:
 	{
 		const char *value;
-		int is_optional;
+		bool is_optional;
 
 		if (unset)
 			value = NULL;
@@ -224,7 +224,7 @@ static enum parse_opt_result do_get_value(struct parse_opt_ctx_t *p,
 
 		is_optional = skip_prefix(value, ":(optional)", &value);
 		if (!value)
-			is_optional = 0;
+			is_optional = false;
 		value = fix_filename(p->prefix, value);
 		if (is_optional && is_missing_file(value)) {
 			free((char *)value);