move abort to before pausing segment loader (#810)

* Fixes an issue where playback can stall when going in/out of fullscreen

@@ -159,6 +159,7 @@ export default class MasterPlaylistController extends videojs.EventTarget {
     });
 
     this.masterPlaylistLoader_.on('mediachanging', () => {
+      this.mainSegmentLoader_.abort();
       this.mainSegmentLoader_.pause();
     });
 
@@ -166,8 +167,6 @@ export default class MasterPlaylistController extends videojs.EventTarget {
       let media = this.masterPlaylistLoader_.media();
       let requestTimeout = (this.masterPlaylistLoader_.targetDuration * 1.5) * 1000;
 
-      this.mainSegmentLoader_.abort();
-
       // If we don't have any more available playlists, we don't want to
       // timeout the request.
       if (this.masterPlaylistLoader_.isLowestEnabledRendition_()) {

@@ -1629,6 +1629,7 @@ QUnit.test('switching playlists with an outstanding key request aborts request a
   keyXhr = this.requests.shift();
   QUnit.ok(!keyXhr.aborted, 'key request outstanding');
 
+  this.player.tech_.hls.playlists.trigger('mediachanging');
   this.player.tech_.hls.playlists.trigger('mediachange');
 
   QUnit.ok(keyXhr.aborted, 'key request aborted');