Use tighter RD bound in try_tx_block_split()

Compression is neutral; small speed gains for some clips tested locally.

STATS_CHANGED

Change-Id: I54d259b928f45268fc59ce156548dcb5168fc85b

av1/encoder/tx_search.c

diff --git a/av1/encoder/tx_search.c b/av1/encoder/tx_search.c
index 2b1fe4d..65b9a24 100644
--- a/av1/encoder/tx_search.c
+++ b/av1/encoder/tx_search.c
@@ -2562,7 +2562,10 @@
       av1_merge_rd_stats(split_rd_stats, &this_rd_stats);
       split_rd_stats->rdcost =
           RDCOST(x->rdmult, split_rd_stats->rate, split_rd_stats->dist);
-      if (no_split_rd < split_rd_stats->rdcost) return;
+      if (split_rd_stats->rdcost > ref_best_rd) {
+        split_rd_stats->rdcost = INT64_MAX;
+        return;
+      }
       block += sub_step;
     }
   }