allow registration without invite link

if signups are allowed invited users should be able to complete their
registration even when they don't have the invite link at hand.

src/api/core/accounts.rs

@@ -101,11 +101,7 @@ async fn register(data: JsonUpcase<RegisterData>, conn: DbConn) -> EmptyResult {
     let mut user = match User::find_by_mail(&email, &conn).await {
         Some(user) => {
             if !user.password_hash.is_empty() {
-                if CONFIG.is_signup_allowed(&email) {
-                    err!("User already exists")
-                } else {
-                    err!("Registration not allowed or user already exists")
-                }
+                err!("Registration not allowed or user already exists")
             }
 
             if let Some(token) = data.Token {
@@ -124,7 +120,7 @@ async fn register(data: JsonUpcase<RegisterData>, conn: DbConn) -> EmptyResult {
             } else if EmergencyAccess::find_invited_by_grantee_email(&email, &conn).await.is_some() {
                 user
             } else if CONFIG.is_signup_allowed(&email) {
-                err!("Account with this email already exists")
+                user
             } else {
                 err!("Registration not allowed or user already exists")
             }