Avoid subtitle disappearing when using subpic queue.

Partialy revert 52a8a396eddcd45f8183cf2f0cc578544f370e18

TODO: Improve subpic queue.
Fix compilation of standalone filters after 3527afd9ec710ab601e25319dddeb482f5001362.

Also move the workaround into its own project.
Always force redraw when the subtitle provider is changed.

There can be cases where the subtitle provider seems to be the same but we need to redraw anyway (e.g. style changes). Since SetSubPicProvider isn't often called, it's not worth making the logic more complex just to save a few redraws.
DVBSub: Fix a stupid parsing bug leading to the wrong page being used.

There is absolutely no reason to copy the region list from the previous page since that means we would just be displaying the old page again instead of the updated one...
DVBSub: Ensure no region is lost to avoid partially rendered subs.

Some regions can be received before they are actually needed. We used to
ignore them but we can need them later so we can't do that.
Update Changelog.txt
DVB and PGS subtitles: Subtitles were sometimes one frame late.

This was invisible most of the time but it could produce blinking in some cases.
DVBSub: "new" throws when memory allocation fails, no need to test against null.

Failure is quite unlikely in those cases and we cannot do much if it ever happens so catching the exception isn't worth it.
MainFrame: adjust the fullscreen size on move
MainFrame: adjust the fullscreen size on open

Fixes #4082
MainFrame: tweak overridden Alt key behaviour

When menubar has focus, we don't receive WM_SYSKEYDOWN messages, only
WM_SYSKEYUP messages. Overriding only show menubar behavior is
reasonable compromise.
Stop mouse hider when entering menu modal loop

We don't receive WM_MOUSELEAVE message until the loop exits
otherwise
Controls: properly remove unused hide ticks

Otherwise we may stay subscribed to periodic timer without a need to
PPageFullscreen: dirty when changing hide policy
Don't read media flags in "delay show not loaded"

They can be whatever
Seekbar: fix possible memory leak
PlayerBar: better way of detecting context menu
PlayerBar: more strict access specifiers
MainFrame: change zorder after reposition

Refs #3980, #4037
MainFrame: show menu after reposition

Refs #4004