WindowServer: Properly determine where a window may be

This also fixes weird behavior of WindowManager::desktop_rect().
None of the callers seem to ever expect an empty Rect, so return a non-empty Rect.

Userland/Services/WindowServer/Window.cpp

@@ -183,7 +183,7 @@ void Window::normalize_rect()
     // For example, the windows that make the desktop rect smaller
     // than the display resolution (e.g. the TaskBar).
     auto min_visible = -1;
-    auto desktop = WindowManager::the().desktop_rect();
+    auto desktop = WindowManager::the().arena_rect_for_type(type())
     auto min_y = 0;
     if (type() == WindowType::Normal) {
         min_size = 50;

Userland/Services/WindowServer/WindowManager.cpp

@@ -1043,7 +1043,7 @@ Gfx::IntRect WindowManager::menubar_rect() const
 Gfx::IntRect WindowManager::desktop_rect() const
 {
     if (active_fullscreen_window())
-        return {};
+        return Screen::the().rect();
     return {
         0,
         menubar_rect().bottom() + 1,
@@ -1052,6 +1052,25 @@ Gfx::IntRect WindowManager::desktop_rect() const
     };
 }
 
+Gfx::IntRect WindowManager::arena_rect_for_type(WindowType type) const
+{
+    switch (type) {
+    case WindowType::Desktop:
+    case WindowType::Normal:
+        return desktop_rect();
+    case WindowType::Menu:
+    case WindowType::WindowSwitcher:
+    case WindowType::Taskbar:
+    case WindowType::Tooltip:
+    case WindowType::Menubar:
+    case WindowType::MenuApplet:
+    case WindowType::Notification:
+        return Screen::the().rect();
+    default:
+        ASSERT_NOT_REACHED();
+    }
+}
+
 void WindowManager::event(Core::Event& event)
 {
     if (static_cast<Event&>(event).is_mouse_event()) {

Userland/Services/WindowServer/WindowManager.h

@@ -120,6 +120,7 @@ public:
 
     Gfx::IntRect menubar_rect() const;
     Gfx::IntRect desktop_rect() const;
+    Gfx::IntRect arena_rect_for_type(WindowType) const;
 
     const Cursor& active_cursor() const;
     const Cursor& hidden_cursor() const { return *m_hidden_cursor; }