[inspector] finish test runner gracefully..

test/inspector/debugger/stepping-with-blackboxed-ranges.js

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 InspectorTest.addScript(
 `function blackboxedBoo()
 {
     var a = 42;
     var b = foo();
     return a + b;
@@ skipping 85 matching lines @@
   }).then(runAction);
 }
 
 var actions = [ "stepOut", "print", "stepOut", "print", "stepOut", "print",
     "stepInto", "print", "stepOver", "stepInto", "print", "stepOver", "stepInto", "print",
     "stepOver", "stepInto", "print" ];
 
 function runAction(response)
 {
   var action = actions.shift();
-  if (!action)
+  if (!action) {
     InspectorTest.completeTest();
+    return;
+  }
 
   if (action === "print") {
     printCallFrames(response.params.callFrames);
     runAction({});
   } else {
     InspectorTest.log("action: " + action);
     Protocol.Debugger[action]();
   }
 }
 
 function printCallFrames(callFrames)
 {
   var topCallFrame = callFrames[0];
   if (topCallFrame.functionName.startsWith("blackboxed"))
     InspectorTest.log("FAIL: blackboxed function in top call frame");
   for (var callFrame of callFrames)
     InspectorTest.log(callFrame.functionName + ": " + callFrame.location.lineNumber + ":" + callFrame.location.columnNumber);
   InspectorTest.log("");
 }