Copter: command-long DO_SET_HOME check first param is zero

Also do not use current location just because lat,lon,alt are all zero

ArduCopter/GCS_Mavlink.cpp

@@ -973,11 +973,15 @@ void GCS_MAVLINK_Copter::handleMessage(mavlink_message_t* msg)
             // param6 : longitude
             // param7 : altitude (absolute)
             result = MAV_RESULT_FAILED; // assume failure
-            if(is_equal(packet.param1,1.0f) || (is_zero(packet.param5) && is_zero(packet.param6) && is_zero(packet.param7))) {
+            if (is_equal(packet.param1,1.0f)) {
                 if (copter.set_home_to_current_location(true)) {
                     result = MAV_RESULT_ACCEPTED;
                 }
             } else {
+                // ensure param1 is zero
+                if (!is_zero(packet.param1)) {
+                    break;
+                }
                 // sanity check location
                 if (!check_latlng(packet.param5, packet.param6)) {
                     break;