Properly reconstruct picked intra block in txk-sel RD search

Skip the quantization and reconstruction process when the best
selected intra mode goes with skip mode. Tested on a few 1080p
key frame coding at mid to high bit-rate range, the encoding
speed is up by 3% - 5%.

The compression for hdres key frame coding is improved from
neutural to 0.3% gains.

Change-Id: Id6b7131e82cdb45e53db65e2b92d8ccfcf00f47e

av1/encoder/encodetxb.c

diff --git a/av1/encoder/encodetxb.c b/av1/encoder/encodetxb.c
index 5cc611d..118f7ec 100644
--- a/av1/encoder/encodetxb.c
+++ b/av1/encoder/encodetxb.c
@@ -2373,7 +2373,7 @@
   x->plane[plane].txb_entropy_ctx[block] = best_txb_ctx;
   x->plane[plane].eobs[block] = best_eob;
 
-  if (!is_inter_block(mbmi)) {
+  if (!is_inter_block(mbmi) && best_eob) {
     // intra mode needs decoded result such that the next transform block
     // can use it for prediction.
     if (cpi->sf.optimize_coefficients != FULL_TRELLIS_OPT) {