Don't automatically switch focus back to a Dialog that is fading out.

Clicking "paste" in the Dialog from the PasteFromWord plugin switches focus
to the editor.  The code added in 49339a0685729c69df92e91138788a6b50cdf2ef was interpreting this
as an accidental focus change, and switching focus back to the dialog, thus
breaking the paste operation.  It was a race condition during the Dialog fade out.

Refs #15370, #16550, #17195.