fix(tabs): hide tab's navbar when a page comes without a navbar

Closes #5556

src/components/content/content.ts

@@ -420,6 +420,7 @@ export class Content extends Ion {
     this._paddingBottom = 0;
     this._headerHeight = 0;
     this._footerHeight = 0;
+    this._tabbarOnTop = null;
 
     let ele: HTMLElement = this._elementRef.nativeElement;
     let parentEle: HTMLElement = ele.parentElement;