Fix signed integer overflow bug

STATS_CHANGED

BUG=aomedia:3112
This commit fix the signed integer overflow bug when pruning modes based on TPL stats are enabled. The bug appeared when both enable_orip and prune_inter_modes_based_on_tpl are enabled.

Change-Id: I720dc5332ad9ad9cecee615f7f5693926d1e7f3d

av1/encoder/rdopt.c

diff --git a/av1/encoder/rdopt.c b/av1/encoder/rdopt.c
index 15046eb..5a8b113 100644
--- a/av1/encoder/rdopt.c
+++ b/av1/encoder/rdopt.c
@@ -2672,6 +2672,7 @@
   // Prune the mode if cur_inter_cost is greater than threshold times
   // best_inter_cost
   const int64_t best_inter_cost = inter_cost_info_from_tpl->best_inter_cost;
+  if (best_inter_cost == INT64_MAX) return 0;
   if (cur_inter_cost >
       ((tpl_inter_mode_prune_mul_factor[prune_level][prune_index] *
         best_inter_cost) >>