Unbreak avcodec_thread_init

avcodec_thread_init currently doesn't do anything at all with pthreads enabled.

libavcodec/pthread.c

@@ -880,7 +880,7 @@ static void validate_thread_parameters(AVCodecContext *avctx)
     }
 }
 
-int ff_thread_init(AVCodecContext *avctx, int thread_count)
+int ff_thread_init(AVCodecContext *avctx)
 {
     if (avctx->thread_opaque) {
         av_log(avctx, AV_LOG_ERROR, "avcodec_thread_init is ignored after avcodec_open\n");

libavcodec/thread.h

@@ -108,7 +108,7 @@ int ff_thread_get_buffer(AVCodecContext *avctx, AVFrame *f);
  */
 void ff_thread_release_buffer(AVCodecContext *avctx, AVFrame *f);
 
-int ff_thread_init(AVCodecContext *s, int thread_count);
+int ff_thread_init(AVCodecContext *s);
 void ff_thread_free(AVCodecContext *s);
 
 #endif /* AVCODEC_THREAD_H */

libavcodec/utils.c

@@ -541,7 +541,7 @@ int attribute_align_arg avcodec_open(AVCodecContext *avctx, AVCodec *codec)
     avctx->frame_number = 0;
 
     if (HAVE_THREADS && !avctx->thread_opaque) {
-        ret = ff_thread_init(avctx, avctx->thread_count);
+        ret = ff_thread_init(avctx);
         if (ret < 0) {
             goto free_and_end;
         }
@@ -1193,8 +1193,7 @@ int av_get_bits_per_sample_format(enum AVSampleFormat sample_fmt) {
 #endif
 
 #if !HAVE_THREADS
-int ff_thread_init(AVCodecContext *s, int thread_count){
-    s->thread_count = thread_count;
+int ff_thread_init(AVCodecContext *s){
     return -1;
 }
 #endif
@@ -1337,7 +1336,9 @@ void ff_thread_await_progress(AVFrame *f, int progress, int field)
 
 int avcodec_thread_init(AVCodecContext *s, int thread_count)
 {
-    return ff_thread_init(s, thread_count);
+    s->thread_count = thread_count;
+    s->thread_type = FF_THREAD_FRAME | FF_THREAD_SLICE;
+    return ff_thread_init(s);
 }
 
 void avcodec_thread_free(AVCodecContext *s)

libavcodec/w32thread.c

@@ -125,7 +125,7 @@ static int avcodec_thread_execute2(AVCodecContext *s, int (*func)(AVCodecContext
     avcodec_thread_execute(s, NULL, arg, ret, count, 0);
 }
 
-int ff_thread_init(AVCodecContext *s, int thread_count){
+int ff_thread_init(AVCodecContext *s){
     int i;
     ThreadContext *c;
     uint32_t threadid;
@@ -135,7 +135,6 @@ int ff_thread_init(AVCodecContext *s, int thread_count){
         return 0;
     }
 
-    s->thread_count= thread_count;
     s->active_thread_type= FF_THREAD_SLICE;
 
     if (thread_count <= 1)