fdo#75118: sw: do not paint zero-width lines

Since commit 6a3fb868b2b8af21f7b6140424b6f8377599a786 zero-width
BorderLinePrimitive2D will actually be painted as hairlines by
VclPixelProcessor2D::tryDrawBorderLinePrimitive2DDirect(), so don't
create such pointless primitives.

(cherry picked from commit 128d3d51c208ec5c37a105ea5c751530bd017d4b)

fdo#75118: actually these are floats, compare with approxEqual

(cherry picked from commit 9fb9fc301502c2762ad4a8059d8d1c818d2843db)

Change-Id: I4c2404b73f106156b83a6d72efa3c8991e5d659e
Reviewed-on: https://gerrit.libreoffice.org/8144
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>