Copter: Loiter clears out pilot acceleration when failsafe occurs

This ensures invalid pilot desired accelerations are cleared from the
loiter controller.  This is probably not strictly necessary because the
vehicle should switch out of Loiter and into RTL during failsafe.

ArduCopter/control_loiter.pde

@@ -45,7 +45,6 @@ static void loiter_run()
         update_simple_mode();
 
         // process pilot's roll and pitch input
-        // To-Do: do we need to clear out feed forward if this is not called?
         wp_nav.set_pilot_desired_acceleration(g.rc_1.control_in, g.rc_2.control_in);
 
         // get pilot's desired yaw rate
@@ -61,6 +60,9 @@ static void loiter_run()
             // clear i term when we're taking off
             set_throttle_takeoff();
         }
+    } else {
+        // clear out pilot desired acceleration in case radio failsafe event occurs and we do not switch to RTL for some reason
+        wp_nav.clear_pilot_desired_acceleration();
     }
 
     // when landed reset targets and output zero throttle