avfilter/dnn_detect: fail on filter if mandatory anchor option is missing

It prevents the filter of running in case such option is missing,
failing early, during init() instead of simply logging an error
during runtime.

Signed-off-by: Leandro Santiago <leandrosansilva@gmail.com>
Reviewed-by: Wenbin Chen <wenbin.chen@intel.com>
Reviewed-by: Guo Yejun <yejun.guo@intel.com>

libavfilter/vf_dnn_detect.c

@@ -173,11 +173,6 @@ static int dnn_detect_parse_yolo_output(AVFrame *frame, DNNData *output, int out
         return AVERROR(EINVAL);
     }
 
-    if (!anchors) {
-        av_log(filter_ctx, AV_LOG_ERROR, "anchors is not set\n");
-        return AVERROR(EINVAL);
-    }
-
     if (output[output_index].dims[1] * output[output_index].dims[2] *
             output[output_index].dims[3] % (box_size * cell_w * cell_h)) {
         av_log(filter_ctx, AV_LOG_ERROR, "wrong cell_w, cell_h or nb_classes\n");
@@ -656,6 +651,14 @@ static av_cold int dnn_detect_init(AVFilterContext *context)
     DnnDetectContext *ctx = context->priv;
     DnnContext *dnn_ctx = &ctx->dnnctx;
     int ret;
+    int using_yolo = (ctx->model_type == DDMT_YOLOV3 ||
+                      ctx->model_type == DDMT_YOLOV4 ||
+                      ctx->model_type == DDMT_YOLOV1V2);
+
+    if (using_yolo && !ctx->anchors) {
+        av_log(ctx, AV_LOG_ERROR, "anchors is not set while being required for YOLO models\n");
+        return AVERROR(EINVAL);
+    }
 
     ret = ff_dnn_init(&ctx->dnnctx, DFT_ANALYTICS_DETECT, context);
     if (ret < 0)