avcodec/dnxhdenc: call slice thread code only if slice threading is enabled

libavcodec/dnxhdenc.c

@@ -526,10 +526,12 @@ FF_DISABLE_DEPRECATION_WARNINGS
 FF_ENABLE_DEPRECATION_WARNINGS
 #endif
 
+    if (avctx->active_thread_type == FF_THREAD_SLICE) {
         if (avctx->thread_count > MAX_THREADS) {
             av_log(avctx, AV_LOG_ERROR, "too many threads\n");
             return AVERROR(EINVAL);
         }
+    }
 
     if (avctx->qmax <= 1) {
         av_log(avctx, AV_LOG_ERROR, "qmax must be at least 2\n");
@@ -537,10 +539,12 @@ FF_ENABLE_DEPRECATION_WARNINGS
     }
 
     ctx->thread[0] = ctx;
+    if (avctx->active_thread_type == FF_THREAD_SLICE) {
         for (i = 1; i < avctx->thread_count; i++) {
             ctx->thread[i] = av_malloc(sizeof(DNXHDEncContext));
             memcpy(ctx->thread[i], ctx, sizeof(DNXHDEncContext));
         }
+    }
 
     return 0;
 fail:  // for FF_ALLOCZ_OR_GOTO