i965: Don't write a counter snapshot on EndTransformFeedback if paused.

i965: Don't write a counter snapshot on EndTransformFeedback if paused.

If the transform feedback object is paused, then we've already written
an ending counter snapshot.  We don't want to write another one.

This fixes assertions in GL33-CTS.transform_feedback.api_errors_test,
which calls EndTransformfeedback after PauseTransformFeedback.  On the
next BeginTransformFeedback, we tried to tally up the results, and saw
an odd number of snapshots (due to the double-end), and tripped an
assertion.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>