Work around WebKit bug 119003 by flushing events when removing a page from a window.
See <https://bugs.webkit.org/show_bug.cgi?id=119003>

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23440 57a11ea4-9604-0410-9ed3-97b8803252fd