pthread_frame: minor simplification to error handling

Get rid of the "ret" variable, and always use err. Report the packet as
consumed if err is unset. This should be equivalent to the old code,
which obviously required err=0 for p->result>=0 (and otherwise,
p->result must have had the value err was last set to). The code block
added by commit 32a5b63126 is also not needed anymore, because the new
code strictly returns err if it's >=0.

Reviewed-by: "Ronald S. Bultje" <rsbultje@gmail.com>

libavcodec/pthread_frame.c

@@ -468,7 +468,7 @@ int ff_thread_decode_frame(AVCodecContext *avctx,
     FrameThreadContext *fctx = avctx->internal->thread_ctx;
     int finished = fctx->next_finished;
     PerThreadContext *p;
-    int err, ret = 0;
+    int err;
 
     /* release the async lock, permitting blocked hwaccel threads to
      * go forward while we are in this function */
@@ -496,7 +496,7 @@ int ff_thread_decode_frame(AVCodecContext *avctx,
     if (fctx->delaying) {
         *got_picture_ptr=0;
         if (avpkt->size) {
-            ret = avpkt->size;
+            err = avpkt->size;
             goto finish;
         }
     }
@@ -542,21 +542,12 @@ int ff_thread_decode_frame(AVCodecContext *avctx,
 
     fctx->next_finished = finished;
 
-    /*
-     * When no frame was found while flushing, but an error occurred in
-     * any thread, return it instead of 0.
-     * Otherwise the error can get lost.
-     */
-    if (!avpkt->size && !*got_picture_ptr)
-        goto finish;
-
     /* return the size of the consumed packet if no error occurred */
-    ret = (p->result >= 0) ? avpkt->size : p->result;
+    if (err >= 0)
+        err = avpkt->size;
 finish:
     async_lock(fctx);
-    if (err < 0)
-        return err;
-    return ret;
+    return err;
 }
 
 void ff_thread_report_progress(ThreadFrame *f, int n, int field)