LibGUI: Remember the maximized value if a window hasn't been created yet

d0fb511d75762e9d97fa80a01585381843b90a0a set the maximized window value
in the File Manager before a window was created, which resulted in crash
everytime you tried to open the program that was closed while it was
maximized. ugh

Here we do more-or-less what GUI::Window::set_rect() does, except we
don't add it to the WindowServer::create_window() IPC call.
That's because the Window Server knows nothing about menus at this
point and just assumes they don't need to be visible.
So if we try to maximize the window then, it could be slightly taller
and a titlebar could be hidden.

So even though it looks how it looks like, it does work and it doesn't
show in the startup size, as described in the mentioned commit (the call
is put a few lines before the initial update()). :^)

Userland/Libraries/LibGUI/Window.cpp

@@ -167,6 +167,7 @@ void Window::show()
         return IterationDecision::Continue;
     });
 
+    set_maximized(m_maximized_when_windowless);
     reified_windows->set(m_window_id, this);
     Application::the()->did_create_window({});
     update();
@@ -998,14 +999,17 @@ void Window::set_forced_shadow(bool shadow)
 bool Window::is_maximized() const
 {
     if (!is_visible())
-        return false;
+        return m_maximized_when_windowless;
 
     return WindowServerConnection::the().is_maximized(m_window_id);
 }
 
 void Window::set_maximized(bool maximized)
 {
-    VERIFY(m_window_id != 0);
+    m_maximized_when_windowless = maximized;
+    if (!is_visible())
+        return;
+
     WindowServerConnection::the().async_set_maximized(m_window_id, maximized);
 }
 

Userland/Libraries/LibGUI/Window.h

@@ -269,6 +269,7 @@ private:
     bool m_resizable { true };
     Optional<Gfx::IntSize> m_resize_aspect_ratio {};
     bool m_minimizable { true };
+    bool m_maximized_when_windowless { false };
     bool m_fullscreen { false };
     bool m_frameless { false };
     bool m_forced_shadow { false };