WindowServer: Add sanity checks to create_window IPC

Author: https://github.com/matthewbjones
Commit: 0ff09d4f74
Pull-request: https://github.com/SerenityOS/serenity/pull/7721
Issue: https://github.com/SerenityOS/serenity/issues/4540

Userland/Services/WindowServer/Window.cpp

@@ -208,7 +208,8 @@ void Window::nudge_into_desktop(bool force_titlebar_visible)
 
 void Window::set_minimum_size(const Gfx::IntSize& size)
 {
-    VERIFY(!size.is_empty());
+    if (size.is_null())
+        return;
 
     if (m_minimum_size == size)
         return;