Fix potential encoder dead-lock after picture resize

The sync interval for the multithreaded encoder was considered as not changing
during the encoding. This is not true if picture size is changed.
The encoder could dead-lock because the main thread and the other threads were
using different sync interval.

Change-Id: I75232bbdbc6c02d77f830d870fd8b4e96697c64e

vp8/encoder/ethreading.c

@@ -59,8 +59,6 @@ THREAD_FUNCTION thread_encoding_proc(void *p_data)
     MB_ROW_COMP *mbri = (MB_ROW_COMP *)(((ENCODETHREAD_DATA *)p_data)->ptr2);
     ENTROPY_CONTEXT_PLANES mb_row_left_context;
 
-    const int nsync = cpi->mt_sync_range;
-
     while (1)
     {
         if (cpi->b_multi_threaded == 0)
@@ -68,6 +66,7 @@ THREAD_FUNCTION thread_encoding_proc(void *p_data)
 
         if (sem_wait(&cpi->h_event_start_encoding[ithread]) == 0)
         {
+            const int nsync = cpi->mt_sync_range;
             VP8_COMMON *cm = &cpi->common;
             int mb_row;
             MACROBLOCK *x = &mbri->mb;