style(esl-mixin-element): simplify subtree check conditions

Co-authored-by: Anna <abarmina@exadel.com>

src/modules/esl-mixin-element/ui/esl-mixin-registry.ts

@@ -69,7 +69,7 @@ export class ESLMixinRegistry {
   public invalidateRecursive(root: HTMLElement = document.body, name?: string): void {
     if (!root) return;
     name ? this.invalidate(root, name) : this.invalidateAll(root);
-    if (!root.children || !root.children.length) return;
+    if (!root.children?.length) return;
     Array.prototype.forEach.call(root.children, (child: Element) => this.invalidateRecursive(child as HTMLElement, name));
   }
 
@@ -174,7 +174,7 @@ export class ESLMixinRegistry {
   private static destroyAll(el: HTMLElement): void {
     const store = (el as any)[STORE] as Record<string, ESLMixinElement> | undefined;
     store && Object.keys(store).forEach((name) => ESLMixinRegistry.destroy(el, name));
-    if (!el.children || !el.children.length) return;
+    if (!el.children?.length) return;
     Array.prototype.forEach.call(el.children, (child: Element) => ESLMixinRegistry.destroyAll(child as HTMLElement));
   }
 }