avcodec/exr: increase vlc depth

Fixes: shift exponent -4 is negative
Fixes: 32265/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_EXR_fuzzer-465133454137753

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

libavcodec/exr.c

@@ -418,7 +418,7 @@ static int huf_decode(VLC *vlc, GetByteContext *gb, int nbits, int run_sym,
 
     init_get_bits(&gbit, gb->buffer, nbits);
     while (get_bits_left(&gbit) > 0 && oe < no) {
-        uint16_t x = get_vlc2(&gbit, vlc->table, 12, 2);
+        uint16_t x = get_vlc2(&gbit, vlc->table, 12, 3);
 
         if (x == run_sym) {
             int run = get_bits(&gbit, 8);