Close button on plotter window is broken

[banesullivan]

When closing a plotter, you currently must press the q button. If you press the exit button in the window, the plotter does not properly closed. For example:

import vtki
from vtki import examples

data = examples.load_uniform()

p = vtki.Plotter(notebook=False)
p.add_mesh(data)
p.show(screenshot='foo.png') # USE EXIT BUTTON NOT Q KEY

which produces a blank image because I guess the renderer is destroyed before the screenshot code is executed:

[akaszynski]

Fixed in b43e2af.