hevc: check slice address length

It is used as get_bits argument and reading 0 bits doesn't make sense.
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavcodec/hevc.c

@@ -532,7 +532,7 @@ static int hls_slice_header(HEVCContext *s)
 
         slice_address_length = av_ceil_log2(s->sps->ctb_width *
                                             s->sps->ctb_height);
-        sh->slice_segment_addr = get_bits(gb, slice_address_length);
+        sh->slice_segment_addr = slice_address_length ? get_bits(gb, slice_address_length) : 0;
         if (sh->slice_segment_addr >= s->sps->ctb_width * s->sps->ctb_height) {
             av_log(s->avctx, AV_LOG_ERROR,
                    "Invalid slice segment address: %u.\n",