fix named constructor completion

pkg/analysis_server/lib/src/services/completion/imported_computer.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 services.completion.computer.dart.toplevel;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analysis_server/src/protocol_server.dart' hide Element,
@@ skipping 149 matching lines @@
   @override
   _ImportedSuggestionBuilder visitNode(AstNode node) {
     return null;
   }
 
   @override
   _ImportedSuggestionBuilder visitPrefixedIdentifier(PrefixedIdentifier node) {
     // Make suggestions for the prefix, but not for the selector
     // InvocationComputer makes selector suggestions
     Token period = node.period;
-    if (period != null && request.offset <= period.offset) {
+    if (period == null || request.offset <= period.offset) {
       return new _ImportedSuggestionBuilder(request, excludeVoidReturn: true);
     }
     return null;
   }
 
   @override
   _ImportedSuggestionBuilder visitPropertyAccess(PropertyAccess node) {
     // Make suggestions for the target, but not for the property name
     // InvocationComputer makes property name suggestions
     var operator = node.operator;
@@ skipping 171 matching lines @@
     addFilteredSuggestions(cache.importedTypeSuggestions);
     addFilteredSuggestions(cache.libraryPrefixSuggestions);
     if (!typesOnly) {
       addFilteredSuggestions(cache.otherImportedSuggestions);
       if (!excludeVoidReturn) {
         addFilteredSuggestions(cache.importedVoidReturnSuggestions);
       }
     }
   }
 }