Render output doesn't fill the entire window

[leoetlino]

For some reason, the render output appears not to fill the entire window anymore; there's always some extra unused space on the right. Manually resizing the window does not work around the bug.

Screenshot:

A bisect points to PR #4940 but I was unable to figure out exactly which commit introduced the issue because several commits do not build.

fcbe5e1ac - (HEAD, refs/bisect/bad) Add a separate thread for rendering and add texture mailbox and shared context to SDL (5 months ago) <James Rowe>
91255b880 - (refs/bisect/skip-91255b8802ac81ddd6012738e92a105865ba8464) Change Qt to use QOpenGLWidget and support shared context and texture mailbox (5 months ago) <James Rowe>
27d0fc64d - (refs/bisect/skip-27d0fc64d03005d3a97ba537a850defdb0e418d3) Add texture mailbox support to opengl renderer. (5 months ago) <James Rowe>
c2e790382 - (refs/bisect/skip-c2e79038252dbf7bbbfbf5aaa09bb5450691186f) Split graphics out of EmuWindow in preparation of shared contexts (5 months ago) <James Rowe>
db7a627a2 - (refs/bisect/skip-db7a627a2e4733d8f60774b7b3894db06a73085a) Add scope acquire context to simplify MakeCurrent and DoneCurrent calls (5 months ago) <James Rowe>
4f19d380f - (refs/bisect/good-4f19d380f53ae630ec437ada6fdad20869f2b533) Merge pull request #4868 from khang06/tex-dump (5 months ago) <James Rowe>

It is very likely that the regression was introduced by 91255b880, though.

I'm still trying to investigate the issue but I suspect the wrong sizes are being passed to UpdateCurrentFramebufferLayout