You shouldn’t. Unless you’re referring to:
Just to be clear: bugs aside, it’s set when another transmission is already scheduled, so you should not run into that condition unless you’re transmitting too much. So: just adhere to the regulations and other limitations and you should not run into that branch of the code at all.
(Aside: note that the LMIC_setTxData2 is commented out in your sample code. So, that code is not sending anything. Also, it’s very unlikely you want the -1 in sizeof(mydata)-1.)