Initialize members and remove unused ones.

Fixes CID #1192565
Fix: MoveVideoWindow() might not be called when needed after 7c6a1ce
("Don't MoveVideoWindow() during fullscreen toggle")

We need to call MoveVideoWindow() to properly handle EC_VIDEO_SIZE_CHANGED event.

Refs #4178
Cosmetics for MoveVideoWindow() method.
Revert "Fix rare black screen issue with madvr"

This reverts commit 455619eadd8c157f977041bdbad4522c47166eb3.

Not reproducible with latest mpc-hc and madvr.
Add wrapper for dynamic winapi function loading
MainFrame: allow unelevated taskbar messages

Fixes #4181
Seekbar: don't rely on system font for metrics

Refs #3997
Subtitle queue: Ensure the queue is invalidated after seeking.

Fixes #3691.
Subtitle queue: Check the invalidation time against the segment end time.

We could miss some subtitles which needed to be invalidated.

Fixes #3691.
PGS Subtitles: Correctly reset the parser after seeking.

Subtitles displayed just after seeking could be wrong.
PGS Subtitles: Ensure the bounding box is correct when the subtitle isn't rendered.

This could cause a black flash if a subtitle failed to render (after seeking for example).

Fixes #3691.
Cosmetic: Remove an unused function.

This was forgotten during a re-factoring long ago.
CompositionObject: Delete the assignment operator for now.

Forbid the use of direct affectation for now, it would be dangerous because of possible leaks and double frees. We could do a deep copy to be safe but it could possibly hurt the performance if we forgot about this and start using affectation a lot.
Statusbar: add minimal height check

In case system font is too small and DLU conversion goes awry.

Refs #3997