max_length must be undefined when using SequenceLabeler

[varisd]

When using SequenceLabeler, the max_length argument must be unset for the underlying encoder (or input_sequence). Otherwise, there will be a shape mismatch in SequenceLabeler.cost for longer training sequences.

This is an ok behaviour, however, there is no indication of this requirement (warning, etc.) which can be quite confusing for the user.

[jlibovicky]

To už mám taky zafixovaný ve větvi.