Floss: Fix btclient tokenization

Using String.split(" ") will get empty strings as tokens as well, for
example in the case of "adapter     show". This fixes this by removing
the empty strings from tokens.

Bug: 238572622
Tag: #floss
Test: Manual - Ran btclient

Change-Id: I24cac5853e09b93625464f134e9c5fbd34d733cd