Call m_menumgr->deletingMenu from quitMenu in addition to destructor

This fixes the bug where noMenuActive() keeps returning false after
closing a menu until the mouse is moved, rendering the keyboard
unusable (the_game calls input->clear() every frame when
noMenuActive() is false).

src/modalMenu.h

@@ -99,6 +99,7 @@ class GUIModalMenu : public gui::IGUIElement
 		allowFocusRemoval(true);
 		// This removes Environment's grab on us
 		Environment->removeFocus(this);
+		m_menumgr->deletingMenu(this);
 		this->remove();
 	}