Fix DesktopSize::is_empty() for the case when only width or only height is 0.

BUG=crbug.com/358909
R=wez@chromium.org

Review URL: https://webrtc-codereview.appspot.com/11479004

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@5867 4adac7df-926f-26a2-2b94-8c16560cd09d
1 file changed