Fix seam in media layer sample

We didn't request the full 360 angle so a black seam was visible.

Author: cabanier

layers-samples/media-layer-sample.html

@@ -145,9 +145,9 @@
         session.requestReferenceSpace('local').then((refSpace) => {
         xrRefSpace = refSpace;
 
-        let angle = 3.1415;
+        let angle = Math.PI;
         if (!video.src.includes("180"))
-          angle *= 2;
+          angle = Math.PI*2;
 
         let layout = "stereo-top-bottom";
         if (video.src.includes("sbs")||video.src.includes("SBS"))