Add NULL check to wireless functions.
Add NULL check to wireless functions.

The old interface_translate_type_to_real function used previously would return OPTX
if it was passed "OPTX" and OPTX existed but was unassigned, whereas get_real_interface returns NULL, so now we
check for NULL.

phil-davis/pfsense,ch1c4um/pfsense,ch1c4um/pfsense,phil-davis/pfsense,pfsense/pfsense,BlackstarGroup/pfsense,brunostein/pfsense,ptorsten/pfsense,dennypage/pfsense,NOYB/pfsense,pfsense/pfsense,ch1c4um/pfsense,NewEraCracker/pfsense,NewEraCracker/pfsense,NewEraCracker/pfsense,NOYB/pfsense,jxmx/pfsense,ptorsten/pfsense,phil-davis/pfsense,brunostein/pfsense,ch1c4um/pfsense,dennypage/pfsense,ptorsten/pfsense,dennypage/pfsense,BlackstarGroup/pfsense,pfsense/pfsense,pfsense/pfsense,NOYB/pfsense,BlackstarGroup/pfsense,jxmx/pfsense,dennypage/pfsense,NewEraCracker/pfsense,brunostein/pfsense,phil-davis/pfsense,BlackstarGroup/pfsense,jxmx/pfsense