Fix import of a new address (without --replace option)

[fsommer]

The execute method does not have a significant result value. The
present variable just contains the cursor object, which is always
true. Therefore the else-case for creating a new address entry can't
be reached.

To fix the behavior we need to fetch the result of the select statement.
If the statement doesn't match anything the fetched result will be
None which evaluates to false and leads to creation of a new address
entry.