type_decoder: update .samplenum before ending .wait() with EOFError

type_decoder: update .samplenum before ending .wait() with EOFError

When the protocol decoder's input data is exhausted, then the .wait()
method will raise the EOFError exception. Python decoders can catch this
exception and handle the condition. For proper annotation emission it is
essential that the self.samplenum value corresponds to the last position
in the input stream. Update it before returning from the .wait() call.