FIX: Missing timezone guess on email session login (#9404)

Timezone is guessed by moment.js if unset upon a normal login, but was not when
logging in via an email link. This adds logic to update a guessed
timezone upon email login so timezones don't end up blank.

app/assets/javascripts/discourse/controllers/email-login.js

@@ -23,7 +23,10 @@ export default Controller.extend({
 
   actions: {
     finishLogin() {
-      let data = { second_factor_method: this.secondFactorMethod };
+      let data = {
+        second_factor_method: this.secondFactorMethod,
+        timezone: moment.tz.guess()
+      };
       if (this.securityKeyCredential) {
         data.second_factor_token = this.securityKeyCredential;
       } else {