Add missed return leading to an NPE

pkg/analysis_server/lib/src/domain_analysis.dart

Index: pkg/analysis_server/lib/src/domain_analysis.dart
diff --git a/pkg/analysis_server/lib/src/domain_analysis.dart b/pkg/analysis_server/lib/src/domain_analysis.dart
index 424815d5095ffc6e0a0a38d511f21b8c2c5d7dd0..391f29927ba558d73ca00175b92c48d600d35bb7 100644
--- a/pkg/analysis_server/lib/src/domain_analysis.dart
+++ b/pkg/analysis_server/lib/src/domain_analysis.dart
@@ -173,6 +173,7 @@ class AnalysisDomainHandler implements RequestHandler {
         server.onFileAnalysisComplete(file);
     if (analysisFuture == null) {
       server.sendResponse(new Response.getNavigationInvalidFile(request));
+      return;
     }
     analysisFuture.then((AnalysisDoneReason reason) async {
       switch (reason) {