This fixes a memleak on an error path (Smatch).

Preserve sizes set by the application and defer erasing as it is not
needed and can cause deadlock between threads with child video windows.

ole32/tests: Mark the draw_continue callbacks as optional. Win9x can skip calls under low-load conditions.

The functionality is a bit questionable in the first place, but there is some
use in the part that limits the maximum reported shader versions.