prefer length over falsy check

Co-authored-by: Jip Frijlink <jipfrijlink@gmail.com>

src/backend/providers/superstream/index.ts

@@ -129,7 +129,7 @@ const convertSubtitles = (subtitleGroup: any): MWCaption | null => {
     })
     .filter(Boolean);
 
-  if (!subtitles.length) return null;
+  if (subtitles.length === 0) return null;
   const subFile = subtitles[0];
   return {
     needsProxy: true,