Copter: protect loiter controller from bad inputs during failsafe

ArduCopter/ArduCopter.pde

@@ -1679,8 +1679,13 @@ void update_roll_pitch_mode(void)
         // apply SIMPLE mode transform
         update_simple_mode();
 
-        // update loiter target from user controls
-        wp_nav.move_loiter_target(g.rc_1.control_in, g.rc_2.control_in, 0.01f);
+        if(failsafe.radio) {
+            // don't allow loiter target to move during failsafe
+            wp_nav.move_loiter_target(0.0f, 0.0f, 0.01f);
+        } else {
+            // update loiter target from user controls
+            wp_nav.move_loiter_target(g.rc_1.control_in, g.rc_2.control_in, 0.01f);
+        }
 
         // copy latest output from nav controller to stabilize controller
         control_roll = wp_nav.get_desired_roll();