Make execution of map-extent's map-projectionchange handler conditional

on the there being a parentLayer._layer property value. This specifically
covers the case when this handler is invoked by the projection change 
event happening, in which the parent layer may be disabled due to a 
media condition and therefore there is no LayerGroup to add the extentLayer
to.

Author: prushforth

src/map-extent.js

@@ -430,27 +430,22 @@ export class HTMLExtentElement extends HTMLElement {
   }
 
   _handleChange() {
-    // parent layer can be disabled due to media query
-    if (!this.parentLayer.disabled) {
-      // add _extentLayer to map if map-extent is checked, otherwise remove it
-      if (this.checked && !this.disabled) {
-        // can be added to mapmllayer layerGroup no matter map-layer is checked or not
-        this._extentLayer.addTo(this.parentLayer._layer);
-        this._extentLayer.setZIndex(
-          Array.from(
-            this.parentLayer.src
-              ? this.parentLayer.shadowRoot.querySelectorAll(
-                  ':host > map-extent'
-                )
-              : this.parentLayer.querySelectorAll(':scope > map-extent')
-          ).indexOf(this)
-        );
-      } else {
-        this.parentLayer._layer?.removeLayer(this._extentLayer);
-      }
-      // change the checkbox in the layer control to match map-extent.checked
-      // doesn't trigger the event handler because it's not user-caused AFAICT
+    // add _extentLayer to map if map-extent is checked, otherwise remove it
+    if (this.checked && !this.disabled && this.parentLayer._layer) {
+      // can be added to mapmllayer layerGroup no matter map-layer is checked or not
+      this._extentLayer.addTo(this.parentLayer._layer);
+      this._extentLayer.setZIndex(
+        Array.from(
+          this.parentLayer.src
+            ? this.parentLayer.shadowRoot.querySelectorAll(':host > map-extent')
+            : this.parentLayer.querySelectorAll(':scope > map-extent')
+        ).indexOf(this)
+      );
+    } else {
+      this.parentLayer._layer?.removeLayer(this._extentLayer);
     }
+    // change the checkbox in the layer control to match map-extent.checked
+    // doesn't trigger the event handler because it's not user-caused AFAICT
   }
   _validateLayerControlContainerHidden() {
     let extentsFieldset = this.parentLayer._propertiesGroupAnatomy;

test/e2e/elements/map-link/map-link-disabled.test.js

@@ -15,10 +15,6 @@ test.describe('map-link disabled', () => {
   });
   test('rel=stylesheet disabled attribute', async () => {
     const viewer = page.getByTestId('viewer');
-    // there's a problem when attempting to select this link by testid. The map-link
-    // code copies all the attributes of the map-link element onto the generated
-    // <link> element it uses to render the content, including the data-testid,
-    // resulting in duplicate ids that mess up the getByTestId algorithm.
     const featuresLink = page.getByTestId('restaurants_templated_link');
     // test that a templated content link can be disabled by the HTML author at
     // page load, and the bounds of the extent do not include the disabled link
@@ -29,6 +25,11 @@ test.describe('map-link disabled', () => {
       maxDiffPixels: 20
     });
     await featuresLink.evaluate((fl) => (fl.disabled = false));
+    // there's a problem when attempting to select this link by testid. The map-link
+    // code copies all the attributes of the map-link element onto the generated
+    // <link> element it uses to render the content, including the data-testid,
+    // resulting in duplicate ids that mess up the getByTestId algorithm.
+    //
     // selecting it this way seems unambiguous at least
     const stylesheetLink = page.locator(
       'map-link[rel=stylesheet][href="restaurants/restaurants.css"]'