Reset current screen ID when IsScreenValid fails.

The current implementation doesn't reset the screen ID-related
member variables when assigning a new source ID fails. This can result in
undefined behavior, including the possibility of displaying incorrect
content in the shared window or screen.

This fix ensures the screen ID is reset to invalid values
when validation fails.

Bug: chromium:347991512
Change-Id: I17e4a6b76caf436e926fb4968144875db03291e2
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/391100
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Alexander Cooper <alcooper@chromium.org>
Commit-Queue: Sunggook Chue <sunggch@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#44612}