Call optimize_b only when enable_optimize_b is on.

This issue isn't triggered currently though, because encode_block() is
always called with enable_optimize_b = 1.

Change-Id: I1ce5a35222cb6a647418bf7e4dc3189db5aa3854

av1/encoder/encodemb.c

@@ -582,6 +582,8 @@ static void encode_block(int plane, int block, int blk_row, int blk_col,
     if (args->enable_optimize_b) {
       av1_xform_quant(cm, x, plane, block, blk_row, blk_col, plane_bsize,
                       tx_size, AV1_XFORM_QUANT_FP);
+      av1_optimize_b(args->cpi, x, plane, blk_row, blk_col, block, plane_bsize,
+                     tx_size, a, l, CONFIG_LV_MAP);
     } else {
       av1_xform_quant(cm, x, plane, block, blk_row, blk_col, plane_bsize,
                       tx_size, AV1_XFORM_QUANT_B);
@@ -593,9 +595,6 @@ static void encode_block(int plane, int block, int blk_row, int blk_col,
 #endif
   }
 
-  av1_optimize_b(args->cpi, x, plane, blk_row, blk_col, block, plane_bsize,
-                 tx_size, a, l, CONFIG_LV_MAP);
-
   av1_set_txb_context(x, plane, block, tx_size, a, l);
 
   if (p->eobs[block]) *(args->skip) = 0;