Wrong coordinate is used in ScreenCapturerWinGdi

Wrong coordinate is used in ScreenCapturerWinGdi in change
https://chromium-review.googlesource.com/c/external/webrtc/+/644787

Bug: webrtc:7950
Change-Id: I8a11a4cedc594ce9c5462578e59b4e31b8c79253
Reviewed-on: https://chromium-review.googlesource.com/655257
Reviewed-by: Jamie Walch <jamiewalch@chromium.org>
Commit-Queue: Zijie He <zijiehe@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#19734}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 9ec5da67f0d529eca0185acebcbb3ef6895c668f