Add missed return leading to an NPE

pkg/analysis_server/lib/src/domain_analysis.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library domain.analysis;
 
 import 'dart:async';
 import 'dart:core';
 
 import 'package:analysis_server/plugin/analysis/analysis_domain.dart';
@@ skipping 155 matching lines @@
               .toResponse(request.id));
         }
       }
       return;
     }
 
     Future<AnalysisDoneReason> analysisFuture =
         server.onFileAnalysisComplete(file);
     if (analysisFuture == null) {
       server.sendResponse(new Response.getNavigationInvalidFile(request));
+      return;
     }
     analysisFuture.then((AnalysisDoneReason reason) async {
       switch (reason) {
         case AnalysisDoneReason.COMPLETE:
           CompilationUnit unit = await server.getResolvedCompilationUnit(file);
           if (unit == null) {
             server.sendResponse(new Response.getNavigationInvalidFile(request));
           } else {
             CompilationUnitElement unitElement = unit.element;
             NavigationCollectorImpl collector = computeNavigation(
@@ skipping 254 matching lines @@
       context.onResultChanged(descriptor).listen((result) {
         StreamController<engine.ResultChangedEvent> controller =
             controllers[result.descriptor];
         if (controller != null) {
           controller.add(result);
         }
       });
     }
   }
 }