Fixes save of existing user for database users (#1574)

* Typecasts $except to int in UniqueUserValue.php

The value of `$except` is a string in a fresh v3 install (for me at least), the identical-to comparison operator therefore means it's not possible to edit an existing user. Typecasting `$except` to an integer fixes this.

* Changes comparison operator to equal to in UniqueUserValue.php

src/Validation/UniqueUserValue.php

@@ -18,6 +18,6 @@ public function validate($attribute, $value, $parameters, $validator)
             return true;
         }
 
-        return $except === $existing->id();
+        return $except == $existing->id();
     }
-}
+}