Fix a crash in WindowCapturereMac when capture() fails.

BUG=http://code.google.com/p/chromium/issues/detail?id=359985
R=sergeyu@chromium.org

Review URL: https://webrtc-codereview.appspot.com/11219004

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@5846 4adac7df-926f-26a2-2b94-8c16560cd09d
1 file changed