Merge pull request #5930 from trongrg/bugfix/ion-infinite-scroll

fix(ion-infinite-scroll): fix error leaving page

ionic/components/content/content.ts

@@ -162,6 +162,7 @@ export class Content extends Ion {
     this.scrollElement.addEventListener(type, handler);
 
     return () => {
+      if (!this.scrollElement) { return; }
       this.scrollElement.removeEventListener(type, handler);
     }
   }