Plane: allow for new guided destination during guided takeoff

if you set a very high alt for takeoff this is useful

ArduPlane/commands.cpp

@@ -99,6 +99,9 @@ void Plane::set_guided_WP(void)
     auto_state.vtol_loiter = false;
     
     loiter_angle_reset();
+
+    // cancel pending takeoff
+    quadplane.guided_takeoff = false;
 }
 
 /*

ArduPlane/quadplane.cpp

@@ -2508,6 +2508,10 @@ bool QuadPlane::in_vtol_mode(void) const
         poscontrol.get_state() > QPOS_APPROACH) {
         return true;
     }
+    if (plane.control_mode == &plane.mode_guided &&
+        guided_takeoff) {
+        return true;
+    }
     if (in_vtol_auto()) {
         if (!plane.auto_state.vtol_loiter || poscontrol.get_state() > QPOS_APPROACH) {
             return true;