ultrahdr: decompress image writes outside bounds for non aligned widths

jpeg_read_raw_data() returns one MCU row per call, and thus one must
pass buffer of at least max_v_samp_factor * DCTSIZE scanlines. The
buffer must be large enough to hold the actual data plus padding
to DCT-block boundaries.

Bug: 283500706
Test: ./ultrahdr_enc_fuzzer

Change-Id: Icb7c7e3eda590efc05d5945e7c906c1e4a012eab