Handle texture non-bounce a bit better.

Handle texture non-bounce a bit better.

This allows us to ignore the texture bounce flag when reading from a
FlatInput, and also handles better the case where an YCbCrInput is read
from multiple times (it's now bounced, which should be better for speed,
I think).

The main motivation, however, is to be able to control sampler state
a bit less hackish in the future.