draw: fix line stippling

draw: fix line stippling

The logic was comparing actual ints, not true/false values.
This meant that it was emitting always multiple line segments instead of just
one even if the stipple test had the same result, which looks inefficient, and
the segments also overlapped thus breaking line aa as well.
(In practice, with the no-op default line stipple pattern, for a 10-pixel
long line from 0-9 it was emitting 10 segments, with the individual segments
ranging from 0-1, 0-2, 0-3 and so on.)

This fixes https://bugs.freedesktop.org/show_bug.cgi?id=94193

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
CC: <mesa-stable@lists.freedesktop.org>