vorbisdec: reject rangebits 0 with non-0 partitions

This causes non-unique elements in floor_setup->data.t1.list, which
makes the stream undecodable according to the specification.

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>