Fix(SVGrenderer): reset svgSize on remove from map (#5966)

so that when the SVG Renderer is re-used and re-added on map, in `_update` method, the check on `_svgSize` triggers and re-assigns `width` and `height` attributes on the `_container`. Otherwise, the latter no longer has width and height, therefore is invisible, until the viewport size is changed.

src/layer/vector/SVG.js

@@ -68,6 +68,7 @@ export var SVG = Renderer.extend({
 		DomEvent.off(this._container);
 		delete this._container;
 		delete this._rootGroup;
+		delete this._svgSize;
 	},
 
 	_onZoomStart: function () {