added warning text box, checked len of list in measurement flagging to prevent error
added warning text box, checked len of list in measurement flagging to prevent error

Caoimhinmg/PmagPy,Caoimhinmg/PmagPy,lfairchild/PmagPy,Caoimhinmg/PmagPy,lfairchild/PmagPy,lfairchild/PmagPy