mesa: return old name for deleted samplers for SAMPLER_BINDING queries

mesa: return old name for deleted samplers for SAMPLER_BINDING queries

If the sampler object has been deleted in the same context the binding
will have been cleared. If it has been deleted in another context, the
spec does not say what should returned. None of the other binding point
queries check for deletion in another context.

Also, as names of deleted objects are free for reuse, the current code
didn't even work reliably.

Reviewed-by: Fredrik Höglund <fredrik@kde.org>
Signed-off-by: Fredrik Höglund <fredrik@kde.org>