Force command line paint code to run again

Merely calling redraw() only requests a redraw request, it's never said
when that paint request might come.

It's only when a dialog pops up (e.g. by clicking File > Exit) that this
repaint would come, leaving the command line in a half-painted state.

Calling update() makes sure that all redraw requests are honored before
returning, making sure that all artifacts are cleared and that our
command line is always on top.

Fixes #375.
Don't call setVisible if component is disposed.
Update commandline UI size if editor is resized.