check email/username syntax before sending it to db

src/Controller/LoginController.php

@@ -157,6 +157,13 @@ class LoginController
             return new JsonContent(['success' => true]);
         }
 
+        if (
+            filter_var(\Container::$request->post('email'), FILTER_VALIDATE_EMAIL) === false &&
+            preg_match('/^[a-zA-Z0-9_\-\.]+$/', \Container::$request->post('email')) !== 1
+        ) {
+            return new JsonContent(['error' => ['errorText' => 'This is not a valid email address or username.']]);
+        }
+
         $user = $this->userRepository->getByEmailOrUsername(\Container::$request->post('email'));
 
         if ($user === null) {
@@ -500,6 +507,13 @@ class LoginController
             }
         }
 
+        if (
+            filter_var(\Container::$request->post('email'), FILTER_VALIDATE_EMAIL) === false &&
+            preg_match('/^[a-zA-Z0-9_\-\.]+$/', \Container::$request->post('email')) !== 1
+        ) {
+            return new JsonContent(['error' => ['errorText' => 'This is not a valid email address or username.']]);
+        }
+
         $user = $this->userRepository->getByEmailOrUsername(\Container::$request->post('email'));
 
         if ($user === null) {