GCS_MAVLink: always allow HOME to be read by MISSION_REQUEST

Fixes #5980

libraries/GCS_MAVLink/GCS_Common.cpp

@@ -337,7 +337,8 @@ void GCS_MAVLINK::handle_mission_request(AP_Mission &mission, mavlink_message_t
         mavlink_mission_request_t packet;
         mavlink_msg_mission_request_decode(msg, &packet);
 
-        if (packet.seq >= mission.num_commands()) {
+        if (packet.seq != 0 && // always allow HOME to be read
+            packet.seq >= mission.num_commands()) {
             // try to educate the GCS on the actual size of the mission:
             mavlink_msg_mission_count_send(chan,msg->sysid, msg->compid, mission.num_commands());
             goto mission_item_send_failed;