av-merge: Use .shift() instead of .pop() in appendQueue for FIFO

.pop() gives LIFO, but FIFO was the intention for appendQueue.
O(n) behavior is fine because appendQueue should be very small.

Signed-off-by: Jesús <heckyel@hyperbola.info>

youtube/static/js/av-merge.js

@@ -164,7 +164,7 @@ function Stream(avMerge, source, startTime, avRatio) {
     });
     this.updateendEvt = addEvent(this.sourceBuffer, 'updateend', (e) => {
         if (this.appendQueue.length != 0) {
-            this.appendSegment(...this.appendQueue.pop());
+            this.appendSegment(...this.appendQueue.shift());
         }
     });
 }