fix showSubtitles flag

Author: domlander

dotcom-rendering/src/components/LoopVideoPlayer.tsx

@@ -236,7 +236,7 @@ export const LoopVideoPlayer = forwardRef(
 							type={source.mimeType}
 						/>
 					))}
-					{subtitleSource !== undefined && (
+					{showSubtitles && (
 						<track
 							// Don't use default - it forces native rendering on iOS
 							default={false}