Fix dialog loading

Author: simonhamp

src/Dialog.php

@@ -110,11 +110,7 @@ public function properties(array $properties): self
 
     public function asSheet(?string $windowId = null): self
     {
-        if (is_null($windowId)) {
-            $this->windowReference = Window::current()->id;
-        } else {
-            $this->windowReference = $windowId;
-        }
+        $this->windowReference = $windowId ?? Window::current()->getId();
 
         return $this;
     }

src/Windows/Window.php

@@ -79,6 +79,11 @@ public function id(string $id = 'main'): self
         return $this;
     }
 
+    public function getId(): string
+    {
+        return $this->id;
+    }
+
     public function title(string $title): self
     {
         $this->title = $title;