Fix crash when loading waypoints from text file while some wpts already existed;
Fix crash when loading waypoints from text file while some wpts already existed;

AutoQuad/qgroundcontrol_aq,AutoQuad/qgroundcontrol_aq,hejunbok/qgroundcontrol_aq,hejunbok/qgroundcontrol_aq,AutoQuad/qgroundcontrol_aq,AutoQuad/qgroundcontrol_aq,hejunbok/qgroundcontrol_aq,hejunbok/qgroundcontrol_aq