swr: Don't crash when encountering a VBO with stride = 0.

swr: Don't crash when encountering a VBO with stride = 0.

The swr driver uses vertex_buffer->stride to determine the number
of elements in a VBO. A recent change to the state-tracker made it
possible for VBO's with stride=0. This resulted in a divide by zero
crash in the driver. The solution is to use the pre-calculated vertex
element stream_pitch in this case.

This patch fixes the crash in a number of piglit and VTK tests introduced
by 17f776c27be266f2.

There are several VTK tests that still crash and need proper handling of
vertex_buffer_index.  This will come in a follow-on patch.

v2: Correctly update all parameters for VBO constants (stride = 0).
    Also fixes the remaining crashes/regressions that v1 did
    not address, without touching vertex_buffer_index.

Reviewed-by: Tim Rowley <timothy.o.rowley@intel.com>