Ensure marker images show if max-width configured

Previous versions of Leaflet had ``.leaflet-container img { max-width: none !important }`` prior to the change in Leaflet@b3ff3a0, when the selector became more specific. 

This change ensures markers continue to be shown in the case of the page loading Leaflet has a CSS rule like ``img { max-width: 100%; }`` applied.

dist/leaflet.css

@@ -44,6 +44,7 @@
 /* .leaflet-container svg: reset svg max-width decleration shipped in Joomla! (joomla.org) 3.x */
 /* .leaflet-container img: map is broken in FF if you have max-width: 100% on tiles */
 .leaflet-container .leaflet-overlay-pane svg,
+.leaflet-container .leaflet-marker-pane img,
 .leaflet-container .leaflet-tile-pane img {
 	max-width: none !important;
 	}