Only attempt to set/remove attribution if control exists

There were multiple places were the existence of the attribution control was checked, but for some code paths, it wasn't checked causing exceptions to be thrown.

Use a single check for the existence of the attribution control at the beginning of setting/removing attribution.

src/Util.js

@@ -174,13 +174,17 @@ export function calcAttributionWidth (map) {
 }
 
 export function setEsriAttribution (map) {
+  if (!map.attributionControl) {
+    return;
+  }
+
   if (!map.attributionControl._esriAttributionLayerCount) {
     map.attributionControl._esriAttributionLayerCount = 0;
   }
 
-  if (map.attributionControl && map.attributionControl._esriAttributionLayerCount === 0) {
+  if (map.attributionControl._esriAttributionLayerCount === 0) {
     // Dynamically creating the CSS rules, only run this once per page load:
-    if (map.attributionControl && !map.attributionControl._esriAttributionAddedOnce) {
+    if (!map.attributionControl._esriAttributionAddedOnce) {
       var hoverAttributionStyle = document.createElement('style');
       hoverAttributionStyle.type = 'text/css';
       hoverAttributionStyle.innerHTML = '.esri-truncated-attribution:hover {' +
@@ -223,8 +227,12 @@ export function setEsriAttribution (map) {
 }
 
 export function removeEsriAttribution (map) {
+  if (!map.attributionControl) {
+    return;
+  }
+
   // Only remove the attribution if we're about to remove the LAST esri-leaflet layer (_esriAttributionLayerCount)
-  if (map.attributionControl && map.attributionControl._esriAttributionLayerCount && map.attributionControl._esriAttributionLayerCount === 1) {
+  if (map.attributionControl._esriAttributionLayerCount && map.attributionControl._esriAttributionLayerCount === 1) {
     map.attributionControl.setPrefix(BASE_LEAFLET_ATTRIBUTION_STRING);
     DomUtil.removeClass(map.attributionControl._container, 'esri-truncated-attribution:hover');
     DomUtil.removeClass(map.attributionControl._container, 'esri-truncated-attribution');