prevent empty tags/formats

src/videos.rs

@@ -129,6 +129,9 @@ impl VideoItem {
         }
     }
     pub fn tags(mut self, tags: Vec<String>) -> Self {
+        if tags.is_empty(){
+            return self;
+        }
         self.tags = Some(tags);
         self
     }
@@ -157,6 +160,9 @@ impl VideoItem {
         self
     }
     pub fn formats(mut self, formats: Vec<VideoFormat>) -> Self {
+        if formats.is_empty(){
+            return self;
+        }
         self.formats = Some(formats);
         self
     }