Let connect() fail with an I/O exception if tag has left the field.

Because connect() can sometimes be implemented without any I/O,
(usually between transitions to/from the NDEF technology),
it does not always notice when a tag has left the field. Since
we promise in the API docs that it does, fix it by checking
(cached) presence.

Change-Id: Ie6ad1b5dec3621051e395d3be0d0e09615e53ebc