If you read my previous post I wrote,
"If you do a level 1 backup and there is no associated level 0 backup, a level 0 backup is taken instead."
A level 0 backup is a full backup, so your question is irrelevant. You can never do a level 1 backup if no level 0 backup exists, as Oracle runs a level 0 backup instead. If you are going to ask questions, please read the answers!