Fix irresponsive button when connecting to an existing site (#13766)

Author: itsmeichigo

RELEASE-NOTES.txt

@@ -9,6 +9,7 @@
 - [*] Home Screen Widget: Tapping on the Orders section of the home screen widget opens the Orders part of the app.
 - [*] Payments: Punctuation updates to error and decline reason messages [https://github.com/woocommerce/woocommerce-ios/pull/13739]
 - [*] Blaze: Display budget field on the dashboard card. [https://github.com/woocommerce/woocommerce-ios/pull/13761]
+- [*] Store picker: fixed the irresponsive Continue button in the site discovery flow. [https://github.com/woocommerce/woocommerce-ios/pull/13766]
 - [*] Products: Fixed a bug where editing the product price did not work as expected, depending on the store's currency settings. [https://github.com/woocommerce/woocommerce-ios/pull/13768]
 - [*] Products: Products can now be created and edited with negative prices. [https://github.com/woocommerce/woocommerce-ios/pull/13776]
 - [**] Blaze: Support evergreen campaign creation. [https://github.com/woocommerce/woocommerce-ios/pull/13684]

WooCommerce/Classes/Authentication/Epilogue/StorePickerViewController.swift

@@ -355,6 +355,7 @@ private extension StorePickerViewController {
     }
 
     func presentSiteDiscovery() {
+        ServiceLocator.authenticationManager.initialize()
         guard let viewController = WordPressAuthenticator.siteDiscoveryUI() else {
             return
         }