Don't try to use the activity bar if it isn't enabled (#63)

Fixes #59

Author: XiangYyang

debug/embedded.html

@@ -26,6 +26,17 @@
                 nulla pariatur. Excepteur sint occaecat cupidatat non proident,
                 sunt in culpa qui officia deserunt mollit anim id est laborum.
             </p>
+            <kicanvas-embed src="examples/pins.kicad_sch" controls="basic">
+            </kicanvas-embed>
+            <p>
+                Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do
+                eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut
+                enim ad minim veniam, quis nostrud exercitation ullamco laboris
+                nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor
+                in reprehenderit in voluptate velit esse cillum dolore eu fugiat
+                nulla pariatur. Excepteur sint occaecat cupidatat non proident,
+                sunt in culpa qui officia deserunt mollit anim id est laborum.
+            </p>
             <kicanvas-embed src="examples/starfish.kicad_pcb" controls="full">
             </kicanvas-embed>
             <p>

src/kicanvas/elements/common/app.ts

@@ -41,7 +41,7 @@ export abstract class KCViewerAppElement<
     ViewerElementT extends ViewerElement,
 > extends KCUIElement {
     #viewer_elm: ViewerElementT;
-    #activity_bar: KCUIActivitySideBarElement;
+    #activity_bar: KCUIActivitySideBarElement | null;
 
     project: Project;
     viewerReady: DeferredPromise<boolean> = new DeferredPromise<boolean>();
@@ -180,7 +180,7 @@ export abstract class KCViewerAppElement<
     protected abstract make_activities(): ElementOrFragment[];
 
     protected change_activity(name?: string) {
-        this.#activity_bar.change_activity(name);
+        this.#activity_bar?.change_activity(name);
     }
 
     protected abstract make_viewer_element(): ViewerElementT;
@@ -208,6 +208,9 @@ export abstract class KCViewerAppElement<
                 ${pre_activities} ${activities} ${post_activities}
             </kc-ui-activity-side-bar>` as KCUIActivitySideBarElement;
             resizer = html`<kc-ui-resizer></kc-ui-resizer>`;
+        } else {
+            // NO activity bar
+            this.#activity_bar = null;
         }
 
         const top_toolbar_buttons = [];