irremote_simpletest show decoded value is None

[njuFerret]

when update irremote from 4.0.6 to 4.1.0, irremote_simletest.py not work as expect.

the member function def decode_bits(self, pulses): of GenericDecode has no return value,

maybe line with return result.code should be added to the last of the function.

[tannewt]

Sounds right to me. Please make a PR and we'll review it. Thanks!