avcodec/utils: the IFF_ILBM implementation assumes that there are a multiple of 16 allocated

Fixes: out of array access
Fixes: 45982/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_IFF_ILBM_fuzzer-5124452659888128
Fixes: 45982/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_IFF_ILBM_fuzzer-6362836707442688

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

libavcodec/utils.c

@@ -317,7 +317,7 @@ void avcodec_align_dimensions2(AVCodecContext *s, int *width, int *height,
     }
 
     if (s->codec_id == AV_CODEC_ID_IFF_ILBM) {
-        w_align = FFMAX(w_align, 8);
+        w_align = FFMAX(w_align, 16);
     }
 
     *width  = FFALIGN(*width, w_align);