avcodec/hevcdsp_template: stay within tables in sao_band_filter()

Fixes: out of array read
Fixes: 47875/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_HEVC_fuzzer-5719393113341952

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

libavcodec/hevcdsp_template.c

@@ -313,7 +313,7 @@ static void FUNC(sao_band_filter)(uint8_t *_dst, uint8_t *_src,
         offset_table[(k + sao_left_class) & 31] = sao_offset_val[k + 1];
     for (y = 0; y < height; y++) {
         for (x = 0; x < width; x++)
-            dst[x] = av_clip_pixel(src[x] + offset_table[src[x] >> shift]);
+            dst[x] = av_clip_pixel(src[x] + offset_table[(src[x] >> shift) & 31]);
         dst += stride_dst;
         src += stride_src;
     }