i965: Fix many of the trivial WebGL demos that broke due to IB optimization.

i965: Fix many of the trivial WebGL demos that broke due to IB optimization.

The index buffer state emit only occurred if there was an IB in place
and we were in either a new batch or a new IB state.  But because we
only flagged new IB state if IB state changed from the last IB state
we calculated, we could simply never emit IB state after batchbuffer
wraps if the first draw didn't use the IB and we didn't actually
change the IB.

Fixes piglit glx-multi-context-ib-1.