draw: fix line stippling with unfilled prims

draw: fix line stippling with unfilled prims

The unfilled stage was not filling in the prim header, and the line stage
then decided to reset the stipple counter or not based on the uninitialized
data. This causes some failures in conform linestipple test (albeit quite
randomly happening depending on environment).
So fill in the prim header in the unfilled stage - I am not entirely sure
if anybody really needs determinant after that stage, but there's at least
later stages (wide line for instance) which copy over the determinant as well.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>