avfilter/dnn_backend_openvino: reduce indentation in free_model_ov

No functional changes except ensures model isn't null.

Signed-off-by: Zhao Zhili <zhilizhao@tencent.com>

libavfilter/dnn/dnn_backend_openvino.c

@@ -463,8 +463,12 @@ static void infer_completion_callback(void *args)
 
 static void dnn_free_model_ov(DNNModel **model)
 {
-    if (*model){
-        OVModel *ov_model = (*model)->model;
+    OVModel *ov_model;
+
+    if (!model || !*model)
+        return;
+
+    ov_model = (*model)->model;
     while (ff_safe_queue_size(ov_model->request_queue) != 0) {
         OVRequestItem *item = ff_safe_queue_pop_front(ov_model->request_queue);
         if (item && item->infer_request) {
@@ -515,7 +519,6 @@ static void dnn_free_model_ov(DNNModel **model)
     av_freep(&ov_model);
     av_freep(model);
 }
-}
 
 
 static int init_model_ov(OVModel *ov_model, const char *input_name, const char *output_name)