do not reset password for LDAP and SAML users or rehash on API calls (#2916)

src/Ldap/LdapUserHydrator.php

@@ -75,9 +75,11 @@ class LdapUserHydrator
         }
 
         // fill them after hydrating account, so they can't be overwritten
-        $user->setPassword('');
+        // by the mapping attributes
+        if ($user->getId() === null) {
+            $user->setPassword('');
+        }
         $user->setAuth(User::AUTH_LDAP);
-
         $user->setPreferenceValue('ldap.dn', $ldapEntry['dn']);
     }