Grid: _previousCenter not reset on show

[Stefaan Van Mieghem]

Use case:

WMS layer not visible
pan or zoom
set layer visible
pan or zoom = layer is briefly (until reloaded) drawn at an offset equal to the previous center - current center.

The previous center being the one at the moment of initialization or when latest visible.


I have added an override on the visible setter in the Grid class to solve the problem:

        override public function set visible(value: Boolean): void {
            super.visible = value;
            if (value && this.map) {
                _previousCenter = this.map.center.clone();
            }
        }