Fix path bug in windows, don't emit code altogether if we have already seen

lib/src/compiler.dart

 // Copyright (c) 2012, 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 compiler;
 
 import 'dart:async';
 import 'dart:collection' show SplayTreeMap;
 import 'dart:json' as json;
 import 'package:analyzer_experimental/src/generated/ast.dart' show Directive, UriBasedDirective;
@@ skipping 89 matching lines @@
 
   /** Compile the application starting from the given [mainFile]. */
   Future run() {
     if (path.basename(_mainPath).endsWith('.dart')) {
       _messages.error("Please provide an HTML file as your entry point.",
           null, file: _mainPath);
       return new Future.immediate(null);
     }
     return _parseAndDiscover(_mainPath).then((_) {
       _analyze();
+      // TODO(jmesserly): need to go through our errors, and figure out if some
+      // of them should be warnings instead.
+      if (_messages.hasErrors) return;
       _transformDart();
       _emit();
-      // TODO(jmesserly): need to go through our errors, and figure out if some
-      // of them should be warnings instead.
-      if (_messages.hasErrors) output.clear();
     });
   }
 
   /**
    * Asynchronously parse [inputFile] and transitively discover web components
    * to load and parse. Returns a future that completes when all files are
    * processed.
    */
   Future _parseAndDiscover(String inputFile) {
     _tasks = new FutureGroup();
@@ skipping 600 matching lines @@
             component.declaringFile.inputPath, messages, options);
         if (styleSheet != null) {
           component.styleSheets.add(styleSheet);
         }
       }
     }
 
     super.visitElementInfo(info);
   }
 }