Do not die if tag has no message

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

parsing.c

@@ -220,7 +220,7 @@ struct taginfo *cgit_parse_tag(struct tag *tag)
 
 	p = data;
 
-	while (p) {
+	while (p && *p) {
 		if (*p == '\n')
 			break;
 
@@ -238,7 +238,7 @@ struct taginfo *cgit_parse_tag(struct tag *tag)
 
 	while (p && (*p == '\n'))
 		p = strchr(p, '\n') + 1;
-	if (p)
+	if (p && *p)
 		ret->msg = xstrdup(p);
 	free(data);
 	return ret;