NPE fix in ExitDetector visitor- in analyzer pkg

pkg/analyzer/test/generated/all_the_rest_test.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.
 
 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine.all_the_rest_test;
 
 import 'dart:collection';
@@ skipping 6874 matching lines @@
   }
 
   void test_assignmentExpression_lhs_throw() {
     _assertTrue("a[throw ''] = 0;");
   }
 
   void test_assignmentExpression_rhs_throw() {
     _assertTrue("v = throw '';");
   }
 
+  void test_await_false() {
+    _assertFalse("await x;");
+  }
+
+  void test_await_throw_true() {
+    _assertTrue("bool b = await (throw '' || true);");
+  }
+
   void test_binaryExpression_and() {
     _assertFalse("a && b;");
   }
 
   void test_binaryExpression_and_lhs() {
     _assertTrue("throw '' && b;");
   }
 
   void test_binaryExpression_and_rhs() {
     _assertTrue("a && (throw '');");
@@ skipping 1964 matching lines @@
     } else {
       expect(scriptSource, isNotNull, reason: "script $scriptIndex");
       String actualExternalScriptName = scriptSource.shortName;
       expect(
           actualExternalScriptName,
           _expectedExternalScriptName,
           reason: "script $scriptIndex");
     }
   }
 }