With no track titles defined, the usage of %t results in unexpected behaviour

[abaumfalk]

Steps to repoduce:

• add CD tracks
• the tracks have no name
• "Destination->By meta data" is chosen
• the destination string contains %t, e.g. "/path/%a - %b/%d.%n-%t"

Expected behaviour:
%t should evaluate to an empty string, all other wildcards replaced as usual

Behaviour of 3.0.1:
a default seems to be used for the file name: "%n - %a - %t" while the path seems unaffected