Check user != nil before checking values (#9881) (#9883)

* Check user != nil before checking values

* Handle autoAdmin

Co-authored-by: zeripath <art27@cantab.net>

models/login_source.go

@@ -473,7 +473,14 @@ func LoginViaLDAP(user *User, login, password string, source *LoginSource, autoR
 	// Update User admin flag if exist
 	if isExist, err := IsUserExist(0, sr.Username); err != nil {
 		return nil, err
-	} else if isExist &&
+	} else if isExist {
+		if user == nil {
+			user, err = GetUserByName(sr.Username)
+			if err != nil {
+				return nil, err
+			}
+		}
+		if user != nil &&
 			!user.ProhibitLogin && len(source.LDAP().AdminFilter) > 0 && user.IsAdmin != sr.IsAdmin {
 			// Change existing admin flag only if AdminFilter option is set
 			user.IsAdmin = sr.IsAdmin
@@ -482,6 +489,7 @@ func LoginViaLDAP(user *User, login, password string, source *LoginSource, autoR
 				return nil, err
 			}
 		}
+	}
 
 	if !autoRegister {
 		if isAttributeSSHPublicKeySet && synchronizeLdapSSHPublicKeys(user, source, sr.SSHPublicKey) {