BfPixelsWrapper: do not store the channel count and pixel type
The RGB channel count and pixel type/byte width can vary for every
series, so it is incorrect to store the values for the first series and
use them for every series.

Fixes ticket #10189.
Merge pull request #684 from melissalinkert/rebased/dev_4_4/buffer-sizes

BfPixelBuffer/BfPixelsWrapper buffer size fixes (rebased onto dev_4_4)