PICDRIVE: make save_frames take ULONG num_frames.
PICDRIVE: fix signed/unsigned warnings and structure sizes.
PICDRIVE: fix PDR version test.
PICDRIVE: fix uninitialised 'bpr' when given bad bits_per_pixel.
PICDRIVE: fix uninitialised 'err' when given count <= 0.
PICDRIVE: fix uninitialised 'pixel_buf' when given bad bits.