Dialog widget doesn't resize

[Douglas Hays]

Make the browser window small and click the first Show Dialog button to show the First Dialog dialog box. The window should be small enough so that the dialog has a horizontal scroll bar. If you close the dialog, make the window bigger, and then open the same dialog it remains the same size it was before, even though the window is bigger. If the dialog is made so small that a horizontal scroll bar appears there doesn't seem to be any way to make the dialog bigger again unless you reload the page.

[Douglas Hays]

(In [16970]) Fixes #8837. Reset width and height in show() so that marginBox returns the correct value.