fix Guest_tuple_generator to handle uneven collections

Signed-off-by: Jan Losinski <losinski@wh2.tu-dresden.de>
Unittest empty GuestTupleGenerators

Signed-off-by: Jan Losinski <losinski@wh2.tu-dresden.de>
Test first round slicing

Signed-off-by: Jan Losinski <losinski@wh2.tu-dresden.de>