fix erroneous dec->status_ setting

We only need to set BITSTREAM_ERROR if !ok.

Change-Id: I5bd13e64797e8bc509477edb29158abb39cb0ee1
Lossless decoding: fix eos_ flag condition

eos_ needs to be set only when superfluous bits have actually
been requested.
Earlier, we were assuming pre-mature end-of-stream to be an error.
Now, more precisely, we mark error when we have encountered end-of-stream *and*
we attempt to read more bits after that.

This handles cases where image data requires no bits to be read

Change-Id: I628e2c39c64f10c443fb51f86b1f5919cc9fd299