Fix X11 is_window_maximized

(cherry picked from commit 59fb6c9ef019933b27c1431fdc01819cda87a248)

platform/x11/os_x11.cpp

@@ -1667,8 +1667,15 @@ bool OS_X11::window_maximize_check(const char *p_atom_name) const {
 
 	if (result == Success) {
 		Atom *atoms = (Atom *)data;
-		Atom wm_act_max_horz = XInternAtom(x11_display, "_NET_WM_ACTION_MAXIMIZE_HORZ", False);
-		Atom wm_act_max_vert = XInternAtom(x11_display, "_NET_WM_ACTION_MAXIMIZE_VERT", False);
+		Atom wm_act_max_horz;
+		Atom wm_act_max_vert;
+		if (strcmp(p_atom_name, "_NET_WM_STATE") == 0) {
+			wm_act_max_horz = XInternAtom(x11_display, "_NET_WM_STATE_MAXIMIZED_HORZ", False);
+			wm_act_max_vert = XInternAtom(x11_display, "_NET_WM_STATE_MAXIMIZED_VERT", False);
+		} else {
+			wm_act_max_horz = XInternAtom(x11_display, "_NET_WM_ACTION_MAXIMIZE_HORZ", False);
+			wm_act_max_vert = XInternAtom(x11_display, "_NET_WM_ACTION_MAXIMIZE_VERT", False);
+		}
 		bool found_wm_act_max_horz = false;
 		bool found_wm_act_max_vert = false;