Fix #1971 hiding the action bar in case of fullscreen video playback

src/main/java/com/owncloud/android/ui/preview/PreviewVideoActivity.java

@@ -104,6 +104,10 @@ public class PreviewVideoActivity extends FileActivity implements OnCompletionLi
           
         // keep the screen on while the playback is performed (prevents screen off by battery save)
         mVideoPlayer.setKeepScreenOn(true);
+
+        if(getSupportActionBar() != null) {
+            getSupportActionBar().hide();
+        }
     }
 
     @Override