svga: Fix the index buffer rebind regression

svga: Fix the index buffer rebind regression

The index buffer handle saved in the hw_state structure could
be invalid after the index buffer is destroyed. Instead of
rebinding the index buffer using the saved index buffer handle,
we will reset the index buffer handle in the hw_state structure
to force resending of the index buffer.

Fixes bug 1593320

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