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@5846 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/modules/desktop_capture/window_capturer_mac.mm

@@ -185,7 +185,6 @@ void WindowCapturerMac::Capture(const DesktopRegion& region) {
       window_id_, kCGWindowImageBoundsIgnoreFraming);
 
   if (!window_image) {
-    CFRelease(window_image);
     callback_->OnCaptureCompleted(NULL);
     return;
   }