[inspector] fixed crash on attempt to access empty scope_info on break

test/inspector/debugger/step-into-arrow.js

+// Copyright 2017 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.log('Checks that stepInto nested arrow function doesn\'t produce crash.');
+
+InspectorTest.setupScriptMap();
+InspectorTest.addScript(`const mult = (x) => (y) =>
+  y ? mult(x * y) : x;
+//# sourceURL=test.js`);
+
+Protocol.Debugger.onPaused(message => {
+  InspectorTest.logCallFrameSourceLocation(message.params.callFrames[0]);
+  Protocol.Debugger.stepInto();
+})
+
+Protocol.Debugger.enable();
+Protocol.Debugger.setBreakpointByUrl({ url: 'test.js', lineNumber: 1 })
+  .then(() => Protocol.Runtime.evaluate({ expression: 'mult(5)(4)()' }))
+  .then(InspectorTest.completeTest);