decoders.status() inserts None into Status object dictionary

[gregoryng]

The decoders.status() function unintentionally inserts attributes into the Status object for tests that aren't named. When you run dir(status_object) on status objects that came from this function, the code throws an exception.

This snippet demonstrates the problem:

import obd

messages = [obd.protocols.protocol.Message(frames=[])]
my_status = obd.decoders.status(messages)

print("type(my_status) =", type(my_status))
# <class 'obd.OBDResponse.Status'>

try:
    dir(my_status)
    exit(1)
except TypeError as excp:
    # '<' not supported between instances of 'NoneType' and 'str'
    print(excp)

# This will contain an entry 'None', which it's not supposed to
print(my_status.__dict__.keys())

The comments in the commit are copied from here:

python-OBD/obd/OBDResponse.py

Lines 91 to 93 in a378bdd

	for name in BASE_TESTS + SPARK_TESTS + COMPRESSION_TESTS:
	if name: # filter out None/reserved tests
	self.__dict__[name] = null_test