i965: Don't replicate data for zero-stride arrays when copying to VBOs.

i965: Don't replicate data for zero-stride arrays when copying to VBOs.

When copy_array_to_vbo_array encountered an array with src_stride == 0
and dst_stride != 0, we would replicate out the single element to the
whole size (max - min + 1).  This is unnecessary: we can simply upload
one copy and set the buffer's stride to 0.

Decreases vertex upload overhead in an upcoming Steam for Linux title.
Prior to this patch, copy_array_to_vbo_array appeared very high in the
profile (Eric quoted 20%).  After the patch, it disappeared completely.

Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>