buffer-controller: avoid using Object.assign() (undefined on Win8.1 -…

… IE11)

src/controller/buffer-controller.js

@@ -222,7 +222,11 @@ class BufferController extends EventHandler {
     let pending = this.segments.reduce( (counter, segment) => (segment.parent === parent) ? counter + 1 : counter , 0);
 
     // this.sourceBuffer is better to use than media.buffered as it is closer to the PTS data from the fragments
-    const bufferedEntries = Object.entries(this.sourceBuffer).map(([k,v]) => [k, v.buffered]);
+    let bufferedEntries = [];
+    const sourceBuffer = this.sourceBuffer;
+    for (let streamType in sourceBuffer) {
+      bufferedEntries.push([streamType, sourceBuffer[streamType].buffered]);
+    }
     const timeRanges = new Map(bufferedEntries);
 
     this.hls.trigger(Event.BUFFER_APPENDED, { parent, pending, timeRanges });