When entering fullscreen, allow for paused state

When entering fullscreen, check if the video is paused and ensure to
display the play button instead.

Signed-off-by: Dean Birch <dean.birch0@gmail.com>

app/src/main/java/com/owncloud/android/ui/preview/PreviewVideoFullscreenDialog.kt

@@ -150,6 +150,9 @@ class PreviewVideoFullscreenDialog(
         }
         mExoPlayer.addListener(playListener)
         playingStateListener = playListener
+
+        // Run once to set initial state of play or pause buttons
+        playListener.onIsPlayingChanged(sourceExoPlayer.isPlaying)
     }
 
     override fun onBackPressed() {