Might be an idea to add a minimum size constrain in window server
instead, since it knows the exact dimensions? But this is a simple fix
that seems to do the job.
- If the GInputBox has a parent and the parent is a GWindow, center the
input box window within the parent window. This looks quite nice.
- Stop processing events in a nested event loop immediately after it's
been asked to quit.
- Fix GWidget::parent_widget() behavior for non-widget parents.
