[fix] utm coord was not initialized in landing module for FW (#3445)

Also
- kill throttle after landing
- add module takoff/land to demo mission flight plan

conf/flight_plans/mission_fw.xml

@@ -1,6 +1,6 @@
 <!DOCTYPE flight_plan SYSTEM "flight_plan.dtd">
 
-<flight_plan alt="260" ground_alt="185" lat0="43.46223" lon0="1.27289" max_dist_from_home="1500" name="Basic" security_height="25" qfu="180">
+<flight_plan alt="260" ground_alt="185" lat0="43.46223" lon0="1.27289" max_dist_from_home="1500" name="Basic" security_height="25" qfu="0">
   <header/>
   <waypoints>
     <waypoint name="HOME" x="0" y="0"/>
@@ -12,6 +12,7 @@
   </waypoints>
   <modules>
     <module name="mission" type="fw"/>
+    <module name="nav" type="takeoff_and_landing"/>
   </modules>
   <exceptions/>
   <blocks>

sw/airborne/modules/nav/nav_takeoff_and_landing_fw.c

@@ -316,6 +316,7 @@ static bool nav_land_run(void)
       break;
     case NAV_LANDING_DONE:
     default:
+      NavKillThrottle();
       landing.status = NAV_LANDING_INIT;
       return false;
   }
@@ -346,7 +347,7 @@ bool nav_land_at_loc(float td_alt, float lat, float lon, float dir, float dist,
     landing.td_id = 0;
     landing.af_id = 0;
     struct LlaCoor_f lla = { RadOfDeg(lat), RadOfDeg(lon), GetAltRef() + td_alt };
-    struct UtmCoor_f utm;
+    struct UtmCoor_f utm = {0};
     utm_of_lla_f(&utm, &lla);
     ENU_OF_UTM_DIFF(landing.td_pos, utm, *stateGetUtmOrigin_f());
     landing.af_pos.x = landing.td_pos.x + dist * sinf(RadOfDeg(dir));