fix: currentTimeDisplay shows 0:00 after seek

Steps to reproduce originally posted by @johanberonius at
videojs#8988 (comment)

- Pause player
- Click progress bar and hold mouse button down
- Current time display is updated correctly
- Release mouse button
- Current time display is reset to zero
- Play video
- Current time display is updated again

This patch integrates to proposed workaround by @johanberonius.

The issue was not caused by adding the option
`disableSeekWhileScrubbingOnMobile` per se, but is a side-effect of the
improvements added in 77c99d2.

Author: phloxic

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

@@ -56,7 +56,7 @@ class SeekBar extends Slider {
     super(player, options);
 
     this.shouldDisableSeekWhileScrubbing_ = shouldDisableSeekWhileScrubbing;
-    this.pendingSeekTime_ = null;
+    this.pendingSeekTime = this.getCurrentTime_;
 
     this.setEventHandlers_();
   }