fix for probing issue
fix for probing issue

The default return value is "MTP:YES", this would trigger for all devices
with no vendor class.

pierrezurek/libmtp,olunx/libmtp,vmandela/libmtp,kbhomes/libmtp-zune,jemc/libmtp,reverendhomer/libmtp,reverendhomer/libmtp,mmalecki/libmtp,philipl/libmtp,Bluerise/libmtp,jemc/libmtp,mmalecki/libmtp,olunx/libmtp,pierrezurek/libmtp,reverendhomer/libmtp,jemc/libmtp,kbhomes/libmtp-zune,olunx/libmtp,Bluerise/libmtp,yifanlu/libMTP,libmtp/libmtp,philipl/libmtp,vmandela/libmtp,jemc/libmtp,reverendhomer/libmtp,libmtp/libmtp,mmalecki/libmtp,yifanlu/libMTP,libmtp/libmtp,philipl/libmtp,Bluerise/libmtp