Fix ignoring large twips values like MSO does (cp#1000087)

which was introduced in 10b4da63e3143108ba75891e9e98fdaa2f7953ab.

Since 1e47614cdb84b018a22a334dad0cdd9f0f53892c, only
convertTwipToMM100Unsigned() ignores large values, which presumably
was not the intention. At least commit message suggests so.

So, move the check back to convertTwipToMM100().

Change-Id: I17040f1987e24789b9de39a837d9f7ecaed520fb
(cherry picked from commit 4d1621136c464b462a598571ecdcfe2ae119d8c7)
Reviewed-on: https://gerrit.libreoffice.org/10177
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>