CC1101 isPromiscuous is broken

[bazuchan]

isPromiscuous implementation sets PreambleLen to 0 here https://github.com/rfquack/RadioLib/blob/master/src/modules/CC1101/CC1101.cpp#L828

which is considered as invalid value https://github.com/rfquack/RadioLib/blob/master/src/modules/CC1101/CC1101.cpp#L687