Fix uninitialized blk_skip for VAR TX.

x->blk_skip used to be uninitialized (leftover from encoding the
previous block), if cm->tx_mode != TX_MODE_SELECT (which is used with
higher --cpu-used or --rt options). This resulted in degraded coding
performance when using cm->tx_mode != TX_MODE_SELECT.

This fixes the VP10/EndToEndTestLarge.EndtoEndPSNRTest/40 unit test.

Also fixed an edge effect where encode_block in encodemb.c used the
formal width of the block (without cropping at the right edge), to
look up blk_skip, while select_tx_block in rdopt.c used the cropped
width to set blk_skip.

Change-Id: I76d0f49ac5ab3ab54203573e0d7fcfcc1c6aa10d

vp10/encoder/encodeframe.c

@@ -3339,6 +3339,15 @@ static void rd_pick_partition(VP10_COMP *cpi, ThreadData *td,
                                bsize >= BLOCK_8X8;
   (void) *tp_orig;
 
+#if CONFIG_VAR_TX
+#ifndef NDEBUG
+  // Nothing should rely on the default value of this array (which is just
+  // leftover from encoding the previous block. Setting it to magic number
+  // when debugging.
+  memset(x->blk_skip[0], 234, sizeof(x->blk_skip[0]));
+#endif  // NDEBUG
+#endif  // CONFIG_VAR_TX
+
   assert(num_8x8_blocks_wide_lookup[bsize] ==
              num_8x8_blocks_high_lookup[bsize]);
 
@@ -4433,7 +4442,6 @@ static void encode_frame_internal(VP10_COMP *cpi) {
   x->quant_fp = cpi->sf.use_quant_fp;
   vp10_zero(x->skip_txfm);
 #if CONFIG_VAR_TX
-  vp10_zero(x->blk_skip);
 #if CONFIG_REF_MV
   vp10_zero(x->blk_skip_drl);
 #endif