Return RequestErrorCode.NO_INDEX_GENERATED for search/refactoring requests.

pkg/analysis_server/lib/src/get_handler.dart

Index: pkg/analysis_server/lib/src/get_handler.dart
diff --git a/pkg/analysis_server/lib/src/get_handler.dart b/pkg/analysis_server/lib/src/get_handler.dart
index c424eaa965dc587d61973217cdddeafa9aa9afea..095ca77c3ec12fff6d34294e31d13f0459c6eed2 100644
--- a/pkg/analysis_server/lib/src/get_handler.dart
+++ b/pkg/analysis_server/lib/src/get_handler.dart
@@ -867,6 +867,9 @@ class GetHandler {
       return _returnFailure(request, 'Analysis server not running');
     }
     Index index = analysisServer.index;
+    if (index == null) {
+      return _returnFailure(request, 'Indexing is disabled');
+    }
     String name = request.uri.queryParameters[INDEX_ELEMENT_NAME];
     if (name == null) {
       return _returnFailure(