Fix #5371: Interface flickers when CEF rendering is resumed

[iManGaaX]

Summary

Since #4634 browsers render with external begin-frame scheduling; in that mode Chromium can hand OnPaint a frame that is still missing composited layers while the compositor rebuilds itself, and MTA uploaded that frame straight to the texture - the interface that was on screen disappeared for a moment and then came back

After a real pause -> resume, the frame that has more to show is now the one that stays on screen: a frame that lost over half of its visible content, or has no visible content at all, is not uploaded; another frame is requested instead, and the complete one is used; the guard gives up after a second, so a page that really became empty is only delayed - never stuck on an old image

The resume path itself is untouched (WasResized/Invalidate/SendExternalBeginFrame from #5202 stay as they are), so this cannot regress #5154

Closes #5371.
The code in the video from: #5371 (comment)

Before ->

2026-09-14.01-09-19.mp4

After ->

2026-09-14.01-26-04.mp4

Checklist

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[FileEX]

I'm updated issue #5371 check it