PLT-4620 fix ios safari private browsing (#4526)

webapp/stores/browser_store.jsx

@@ -203,9 +203,13 @@ class BrowserStoreClass {
     }
 
     hasSeenLandingPage() {
+        if (this.isLocalStorageSupported()) {
             return JSON.parse(sessionStorage.getItem('__landingPageSeen__'));
         }
 
+        return true;
+    }
+
     setLandingPageSeen(landingPageSeen) {
         return sessionStorage.setItem('__landingPageSeen__', JSON.stringify(landingPageSeen));
     }