Fix rare hang in multi-thread encoder on Windows

This patch is to fix a rare hang in multi-thread encoder that was
only seen on Windows. Thanks for John's help in debugging the
problem. More test is needed.

Change-Id: Idb11c6d344c2082362a032b34c5a602a1eea62fc

vp8/encoder/ethreading.c

diff --git a/vp8/encoder/ethreading.c b/vp8/encoder/ethreading.c
index c00494d..c92a366 100644
--- a/vp8/encoder/ethreading.c
+++ b/vp8/encoder/ethreading.c
@@ -514,6 +514,7 @@
             LPFTHREAD_DATA * lpfthd = &cpi->lpf_thread_data;
 
             sem_init(&cpi->h_event_start_lpf, 0, 0);
+            sem_init(&cpi->h_event_end_picklpf, 0, 0);
             sem_init(&cpi->h_event_end_lpf, 0, 0);
 
             lpfthd->ptr1 = (void *)cpi;
@@ -547,6 +548,7 @@
 
         sem_destroy(&cpi->h_event_end_encoding);
         sem_destroy(&cpi->h_event_end_lpf);
+        sem_destroy(&cpi->h_event_end_picklpf);
         sem_destroy(&cpi->h_event_start_lpf);
 
         //free thread related resources

vp8/encoder/onyx_if.c

diff --git a/vp8/encoder/onyx_if.c b/vp8/encoder/onyx_if.c
index 1738e56..78f8655 100644
--- a/vp8/encoder/onyx_if.c
+++ b/vp8/encoder/onyx_if.c
@@ -3140,7 +3140,7 @@
 
 #if CONFIG_MULTITHREAD
     if (cpi->b_multi_threaded)
-        sem_post(&cpi->h_event_end_lpf); /* signal that we have set filter_level */
+        sem_post(&cpi->h_event_end_picklpf); /* signal that we have set filter_level */
 #endif
 
     if (cm->filter_level > 0)
@@ -4135,7 +4135,7 @@
 #if CONFIG_MULTITHREAD
     /* wait that filter_level is picked so that we can continue with stream packing */
     if (cpi->b_multi_threaded)
-        sem_wait(&cpi->h_event_end_lpf);
+        sem_wait(&cpi->h_event_end_picklpf);
 #endif
 
     // build the bitstream

vp8/encoder/onyx_int.h

diff --git a/vp8/encoder/onyx_int.h b/vp8/encoder/onyx_int.h
index e2e6b36..c2fcff8 100644
--- a/vp8/encoder/onyx_int.h
+++ b/vp8/encoder/onyx_int.h
@@ -590,6 +590,7 @@
     sem_t *h_event_start_encoding;
     sem_t h_event_end_encoding;
     sem_t h_event_start_lpf;
+    sem_t h_event_end_picklpf;
     sem_t h_event_end_lpf;
 #endif