avcodec/tiff: Use av_fast_padded_malloc() in tiff_unpack_fax()

Fixes: Timeout
Fixes: 1213/clusterfuzz-testcase-minimized-6022987469815808

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
