Don't allow challenges with no participating cards
Don't allow challenges with no participating cards

cryogen/throneteki,ystros/throneteki,samuellinde/throneteki,samuellinde/throneteki,cryogen/gameteki,jeremylarner/ringteki,DukeTax/throneteki,Antaiseito/throneteki_for_doomtown,cavnak/throneteki,gryffon/ringteki,gryffon/ringteki,cryogen/gameteki,jeremylarner/ringteki,jbrz/throneteki,jbrz/throneteki,jeremylarner/ringteki,Antaiseito/throneteki_for_doomtown,DukeTax/throneteki,cavnak/throneteki,gryffon/ringteki,cryogen/throneteki