P1, P2, and P3 are respectively the text versions of PBM, PGM and PPM
files.
We can not obtain the buffer size using av_imgage_get_buffer_size() as
every pixel in the picture will occupy a random size between 16 and 32
bits ("4 " and "231 " are such example).
Ideally, we could look for the next header (or EOF) in the bytestream,
but this commit is meant to fix a decoding regression introduced by
48ac4532d4.
Fix Ticket #5670
None of these symbols should be accessed directly, so declare them as
hidden.
Signed-off-by: Mans Rullgard <mans@mansr.com>
(cherry picked from commit d36beb3f69)