IndexPreloadingUtil: Fix warning about missing cases in switch block

Signed-off-by: Edwin Kempin <ekempin@google.com>
Change-Id: I7c50efc282f6c5c9e886eebdd153ad92f644eda8

java/com/google/gerrit/httpd/raw/IndexPreloadingUtil.java

@@ -162,6 +162,8 @@ public class IndexPreloadingUtil {
       case DIFF:
         matcher = DIFF_URL_PATTERN.matcher(requestedURL);
         break;
+      case DASHBOARD:
+      case PAGE_WITHOUT_PRELOADING:
       default:
         return Optional.empty();
     }