Don't copy thread data for the main thread.

Change-Id: I6adee6704cacfeae0ed0b217a91095457d1be74a

vp9/encoder/vp9_ethread.c

@@ -119,10 +119,14 @@ void vp9_encode_tiles_mt(VP9_COMP *cpi) {
     thread_data = (EncWorkerData*)worker->data1;
 
     // Before encoding a frame, copy the thread data from cpi.
+    if (thread_data->td != &cpi->td) {
       thread_data->td->mb = cpi->td.mb;
       thread_data->td->rd_counts = cpi->td.rd_counts;
+    }
+    if (thread_data->td->counts != &cpi->common.counts) {
       vpx_memcpy(thread_data->td->counts, &cpi->common.counts,
                  sizeof(cpi->common.counts));
+    }
 
     // Handle use_nonrd_pick_mode case.
     if (cpi->sf.use_nonrd_pick_mode) {