there's no lokdocview property to tell if the doc has been completely
initialized (initializeForRendering() has been called, etc.). This new
property takes care of that which we now use to ignore
configure event fired before document is initialized for rendering.
Configure event handler queries document for row/col header which
asserts because some values hasn't been initialized yet.

Change-Id: I58385b2cb56bf317fe20ecf0570b7095f7260174
Reviewed-on: https://gerrit.libreoffice.org/51156Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: pranavk <pranavk@collabora.co.uk>