Fix ScreenCapturerWinGdi to handle DesktopFrameWin::Create() errors.

DesktopFrameWin::Create() may return nullptr when it fails to allocate
windows bitmap. ScreenCapturerWinGdi wasn't handling that case properly.

BUG=527660

Review URL: https://codereview.webrtc.org/1309143007

Cr-Commit-Position: refs/heads/master@{#9865}
1 file changed