Ignore invalid mouse cursor image

webrtc/modules/desktop_capture/mouse_cursor_monitor_mac.mm

 /*
  *  Copyright (c) 2013 The WebRTC 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 in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 238 matching lines @@
   // TODO(zijiehe): Remove this overload.
   callback_->OnMouseCursorPosition(state, position);
   callback_->OnMouseCursorPosition(
       position.subtract(configuration.bounds.top_left()));
 }
 
 void MouseCursorMonitorMac::CaptureImage(float scale) {
   NSCursor* nscursor = [NSCursor currentSystemCursor];
 
   NSImage* nsimage = [nscursor image];
+  if (!nsimage.isValid) {

[Jamie, 2017/08/07 21:49:34]

According to
https://developer.apple.com/documentation/appkit/nscursor/1527062-image?langu...,
this will return nil if invalid. I'm not sure if isValid returns false if you
call it on nil, or if it will still crash, but it seems like a nil check might
be a better option here.

[Hzj_jie, 2017/08/07 23:22:33]

Done.

+    return;
+  }
   NSSize nssize = [nsimage size];  // DIP size
 
   // No need to caputre cursor image if it's unchanged since last capture.
   if ([[nsimage TIFFRepresentation] isEqual:[last_cursor_ TIFFRepresentation]]) return;
   last_cursor_ = nsimage;
 
   DesktopSize size(round(nssize.width * scale),
                    round(nssize.height * scale));  // Pixel size
   NSPoint nshotspot = [nscursor hotSpot];
   DesktopVector hotspot(
@@ skipping 61 matching lines @@
   return new MouseCursorMonitorMac(options, kCGNullWindowID, screen);
 }
 
 std::unique_ptr<MouseCursorMonitor> MouseCursorMonitor::Create(
     const DesktopCaptureOptions& options) {
   return std::unique_ptr<MouseCursorMonitor>(
       CreateForScreen(options, kFullDesktopScreenId));
 }
 
 }  // namespace webrtc