Return a count of zero if you're missing a count node but have a RETS-STATUS node with code 20201 indicating no records found

Offutt RETS server at http://rets.offutt-innovia.com:8080/wnc/login gives this sometimes when requesting a count:

```<RETS ReplyCode="0" ReplyText="Operation Successful">
<RETS-STATUS ReplyCode="20201" ReplyText="No matching records were found" />
</RETS>```

was causing this error:

NoMethodError: undefined method `attr' for nil:NilClass
    /Users/Dan/Dev/rets/lib/rets/parser/compact.rb:52:in `get_count'

http://www.reso.org/assets/RETS/Specifications/rets_1_7_2.pdf section 3.5 indicates the above is probably a valid response:
The rets-status MAY be included in the response if the ReplyCode or ReplyText given in the body-start-line becomes invalid during the creation of the response. If the server includes a rets-status in its reply, the client MUST use the ReplyCode and ReplyText from the rets-status rather than from the body-start-line.

I think that response should return a valid count of zero. See test.