The pixel buffer base address is never unlocked this causes
a bug with some pixel format types that are produced natively
by the hardware decoder: the first buffer was always used.
Unlock the pixel buffer base address fixes the issue.
(cherry picked from commit c06fdacc3dc706e70d953917fea845532d3703ca)
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>