bnc#822347: if number type is not set, skip numbering

If numbering is detected then (level is > 0) and the number type
is not set, the defult bullet symbol is written. This is not
correct as the default should be SVX_NUM_NUMBER_NONE which should
skip numbering or set it to none. With this change the numbering
is skipped (as in MSO).

(cherry picked from commit 14fa2698f2f651343675761e75be01b84c4c5ff1)

Conflicts:
	oox/source/export/drawingml.cxx

Change-Id: I8d08a6325509c7bd6f96f64c8d29e5f3045458ca
Reviewed-on: https://gerrit.libreoffice.org/11181
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>