Ignore invalid mouse cursor image

webrtc/modules/desktop_capture/mouse_cursor_monitor_mac.mm

Index: webrtc/modules/desktop_capture/mouse_cursor_monitor_mac.mm
diff --git a/webrtc/modules/desktop_capture/mouse_cursor_monitor_mac.mm b/webrtc/modules/desktop_capture/mouse_cursor_monitor_mac.mm
index 2bb06b7b4bcb0ce599ed1f7c5ef194fbc94b9f1b..b1917a0e209cd4228b3933794412e9a1a9a0d519 100644
--- a/webrtc/modules/desktop_capture/mouse_cursor_monitor_mac.mm
+++ b/webrtc/modules/desktop_capture/mouse_cursor_monitor_mac.mm
@@ -256,6 +256,9 @@ 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.