With a bad timing in wx:batch() the driver could get stuck
handling commands without ever checking for gui events.

Avoid that by exiting loop after the driver have done cond_wait a
couple of times.

Enable window to handle drop file events.

There seems to be a timeing dependent double delete when doing
reference cleanup after wx:destroy(). wxGraphicsObjects can thus not
be free'ed by wx in the cleanup phase. A guess is that the underlying
rendering context deletes all graphics objects without careeing about
wxWidgets reference counting.

Bitmaps of size less than 1 generates asserts,
and size 0 event is before window is realized.