Handle some video playback error edge cases a bit better

Author: jannenikula

android/sources/src/com/unity3d/ads/android/video/UnityAdsVideoPlayView.java

@@ -585,16 +585,18 @@ private class VideoStateChecker extends TimerTask {
 
 		@Override
 		public void run () {
-			if (_videoView == null || _timeLeftInSecondsText == null)
-				this.cancel();
-			
+			if (_videoView == null || _timeLeftInSecondsText == null) {
+				purgeVideoPausedTimer();
+				return;
+			}
+
 			PowerManager pm = (PowerManager)getContext().getSystemService(Context.POWER_SERVICE);			
 			if (!pm.isScreenOn()) {
 				pauseVideo();
 			}
-			
+
 			_oldPos = _curPos;
-			
+
 			try {
 				_curPos = Float.valueOf(_videoView.getCurrentPosition());
 			}