Copter: reduce throttle to min once landed in RTL

This catches the case where the vehicle lands but the user doesn't
immediately put the throttle to zero.  Before this check it would
continue to attempt to hold it's

ArduCopter/control_rtl.pde

@@ -325,12 +325,27 @@ static void rtl_land_run()
     int16_t roll_control = 0, pitch_control = 0;
     float target_yaw_rate = 0;
     // if not auto armed set throttle to zero and exit immediately
-    if(!ap.auto_armed || !inertial_nav.position_ok()) {
+    if(!ap.auto_armed || ap.land_complete) {
         attitude_control.relax_bf_rate_controller();
         attitude_control.set_yaw_target_to_current_heading();
         attitude_control.set_throttle_out(0, false);
         // set target to current position
         wp_nav.init_loiter_target();
+
+#if LAND_REQUIRE_MIN_THROTTLE_TO_DISARM == ENABLED
+        // disarm when the landing detector says we've landed and throttle is at minimum
+        if (ap.land_complete && (g.rc_3.control_in == 0 || failsafe.radio)) {
+            init_disarm_motors();
+        }
+#else
+        // disarm when the landing detector says we've landed
+        if (ap.land_complete) {
+            init_disarm_motors();
+        }
+#endif
+
+        // check if we've completed this stage of RTL
+        rtl_state_complete = ap.land_complete;
         return;
     }
 
@@ -365,18 +380,6 @@ static void rtl_land_run()
 
     // check if we've completed this stage of RTL
     rtl_state_complete = ap.land_complete;
-
-#if LAND_REQUIRE_MIN_THROTTLE_TO_DISARM == ENABLED
-    // disarm when the landing detector says we've landed and throttle is at minimum
-    if (ap.land_complete && (g.rc_3.control_in == 0 || failsafe.radio)) {
-        init_disarm_motors();
-    }
-#else
-    // disarm when the landing detector says we've landed
-    if (ap.land_complete) {
-        init_disarm_motors();
-    }
-#endif
 }
 
 // get_RTL_alt - return altitude which vehicle should return home at