Fix some video -> framebuffer issues

[unknownbrackets]

This kills some of the flicker and size problems with videos, and even a missing video (#3771, #4273.)

It's still not perfect. As noted in #4270 (comment), some games don't use the fbo for both video frames. The result is that some filtering is slightly different, so you see very slight artifacts. The effect of this reduces at higher rendering resolutions (or did for me anyway.)

Anyway, this is a lot better already. That said, I could use testing on more games (@solarmystic, wanna test a few?)

-[Unknown]

[daniel229]

Fixed video render at that render resolution : windows size not 1:1 like God of War,Super Robot Taisen OE.

[danyalziakhan]

@unknownbrackets your commit slightly improves the intro video playback in MGS:Portable Ops. Now, it doesn't change viewport at non-1x resolution at 1x window size, However, it still flickers (changes viewport) at Full Screen (or non-1x window size) at non-1x resolution.

Another improvement is that now the video plays okay (by okay I mean the effect is same as I described above without shader) without showing black screen with "Scanlines (CRT)" shader that are being drawn at "Output Resolution".

[unknownbrackets]

Hmm, it fixed other games that had viewport issues at non-1x, that's odd. Is the video in the bottom left corner of the window, or too big in these scenarios?

-[Unknown]

[danyalziakhan]

It's neither small nor too big. At Full screen with 2x Internal resolution, the video flickers and the viewport squashes a bit. Not sure if the screenshot can help:- (taken through Print Screen)

@solarmystic and @thedax can confirm this, I guess.

[solarmystic]

@unknownbrackets

Will do the usual tests and report back later, with the usual tables etc.

[solarmystic]

@unknownbrackets @hrydgard

Test results:

Major Observations:

1. Mostly nothing worthy of note in my list. Which is good, as all the games in that list had no prior flickering issues reported in the current master (no regressions from master). With the exception of Tekken 5 (see below)
2. Tekken 5 Dark Resurrection has never displayed its opening FMV before in any previous master, which I noted in the list. No regression there.
3. However, as per @DanyalZia's suggestion, testing MGS Portable Ops (not in the test suite, but I have the game) yields comparable results as he outlined above. MGS Peace Walker is obviously not afflicted with same issue, as already noted in my list.

Conclusion:
This commit does not negatively affect any game in the test suite with regards to FMV playback/graphics and is thus safe for merging at least for the games in my list.

[unknownbrackets]

Cool, thanks for testing. I wonder what's up with Tekken 5.

Hmm, maybe something still isn't being reset for Metal Gear Solid...

-[Unknown]