feat: Eigenschaften zu LogInDto für Validierung und Null-Prüfungen hinzugefügt

WorkFlow.API/Models/LoginDto.cs

@@ -1,4 +1,9 @@
 namespace WorkFlow.API.Models
 {
-    public record LogInDto(int? UserId, string? Username, string Password);
+    public record LogInDto(int? UserId, string? Username, string Password)
+    {
+        public bool HasUserId => UserId is not null;
+        public bool HasUsername => Username is not null;
+        public bool IsInvalid => !HasUserId && !HasUsername;
+    };
 }