fix: update the progress-bar correctly when pausing the video and cli…

…ck the seek-bar.

First,when handle mosue down event of the seek-bar, we set player's scrubbing_ to true, and at the same tick, the update function called and we call super.update(). however, it returns undefined because the progress equals to the previous progress, the root cause is that we get cached currentTime. So we call super.update() in the next tick to make sure we can get the correct progress.Second, when toggle visibility of the document,we should not call this.enableInterval_() when the player is paused or waiting.
Fixed videojs#6232

src/js/control-bar/progress-control/seek-bar.js

@@ -78,7 +78,9 @@ class SeekBar extends Slider {
     if (document.hidden) {
       this.disableInterval_(e);
     } else {
-      this.enableInterval_();
+      if (!this.player_.paused() && !this.player_.hasClass('vjs-waiting')) {
+        this.enableInterval_();
+      }
 
       // we just switched back to the page and someone may be looking, so, update ASAP
       this.update();
@@ -133,9 +135,8 @@ class SeekBar extends Slider {
    *          The current percent at a number from 0-1
    */
   update(event) {
-    const percent = super.update();
-
     this.requestAnimationFrame(() => {
+      const percent = super.update();
       const currentTime = this.player_.ended() ?
         this.player_.duration() : this.getCurrentTime_();
       const liveTracker = this.player_.liveTracker;
@@ -167,8 +168,6 @@ class SeekBar extends Slider {
         this.duration_ = duration;
       }
     });
-
-    return percent;
   }
 
   /**