Minor robustness fixes for Bokeh models (#8270)

Author: philippjfr

panel/models/ace.ts

@@ -126,7 +126,9 @@ export class AcePlotView extends HTMLBoxView {
   }
 
   _update_theme(): void {
-    this._editor.setTheme(`ace/theme/${this.model.theme}`)
+    if (this._editor) {
+      this._editor.setTheme(`ace/theme/${this.model.theme}`)
+    }
   }
 
   _update_filename(): void {

panel/models/react_component.ts

@@ -92,7 +92,7 @@ export class ReactComponentView extends ReactiveESMView {
     this._force_update_callbacks = []
     if (this.react_root && this.use_shadow_dom) {
       super.remove()
-      this.react_root.then((root: any) => root.unmount())
+      this.react_root.then((root: any) => root && root.unmount())
     } else {
       this._applied_stylesheets.forEach((stylesheet) => stylesheet.uninstall())
       for (const cb of (this._lifecycle_handlers.get("remove") || [])) {