avcodec/hevc_ps: Check num_long_term_ref_pics_sps

Fixes out of array access
Fixes: signal_sigsegv_35bd0f0_1182_cov_791726764_STRUCT_B_Samsung_4.bit
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/hevc_ps.c

@@ -951,6 +951,11 @@ int ff_hevc_decode_nal_sps(HEVCContext *s)
     sps->long_term_ref_pics_present_flag = get_bits1(gb);
     if (sps->long_term_ref_pics_present_flag) {
         sps->num_long_term_ref_pics_sps = get_ue_golomb_long(gb);
+        if (sps->num_long_term_ref_pics_sps > 31U) {
+            av_log(0, AV_LOG_ERROR, "num_long_term_ref_pics_sps %d is out of range.\n",
+                   sps->num_long_term_ref_pics_sps);
+            goto err;
+        }
         for (i = 0; i < sps->num_long_term_ref_pics_sps; i++) {
             sps->lt_ref_pic_poc_lsb_sps[i]       = get_bits(gb, sps->log2_max_poc_lsb);
             sps->used_by_curr_pic_lt_sps_flag[i] = get_bits1(gb);