Using a non-null background brush does remove an initial white flash
while the program is loading and before we start painting. But this
results in some extra and unnecessary redraws. Default WM_ERASEBKGND
behaviour is to do nothing if this is brush is null, so if non-null we
get erased and must redraw. Suppressing WM_ERASEBKGND will not give us
that initial paint, so no benefit in keeping the brush added in #115968.
Pull Request: https://projects.blender.org/blender/blender/pulls/116642
355654487e