Return a 404 if attempting to delete a user that does not exist; closes pterodactyl#503

Author: DaneEveritt

app/Repositories/UserRepository.php

@@ -151,6 +151,8 @@ public function update($id, array $data)
      */
     public function delete($id)
     {
+        $user = Models\User::findOrFail($id);
+
         if (Models\Server::where('owner_id', $id)->count() > 0) {
             throw new DisplayException('Cannot delete a user with active servers attached to thier account.');
         }
@@ -170,7 +172,7 @@ public function delete($id)
                 $subuser->delete();
             }
 
-            Models\User::destroy($id);
+            $user->delete();
             DB::commit();
         } catch (\Exception $ex) {
             DB::rollBack();