return 404 if snapshot is not found

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

ui-snapshot.c

@@ -175,11 +175,13 @@ void cgit_print_snapshot(const char *head, const char *hex,
 
 	if (!hex && dwim) {
 		hex = get_ref_from_filename(ctx.repo->url, filename, f);
-		if (hex != NULL) {
+		if (hex == NULL) {
+			html_status(404, "Not found", 0);
+			return;
+		}
 		prefix = xstrdup(filename);
 		prefix[strlen(filename) - strlen(f->suffix)] = '\0';
 	}
-	}
 
 	if (!hex)
 		hex = head;