Fix hinv.ncpu and hinv.ndisk as first Windows PMDA fetch.
Fix hinv.ncpu and hinv.ndisk as first Windows PMDA fetch.

If the very first fetch to a newly started Windows PMDA is
either hinv.ncpu or hinv.ndisk, zero could be returned.

This happened because these two were relying on other metrics
to populate the disk/CPU instance domain, and they then just
returned the count.  Added some logic to say "if we haven't
had some other metric ID cover this for us, then explicitly
populate the instance domain" for these metrics.

wuliming/pcp,ryandoyle/pcp_original,edwardt/pcp,mbaldessari/pcp,ryandoyle/pcp_original,tjanez/pcp,aeg-aeg/pcpfans,prasincs/pcp,aeg-aeg/pcpfans,prasincs/pcp,tjanez/pcp,ryandoyle/pcp_original,wuliming/pcp,mbaldessari/pcp,adfernandes/pcp,tjanez/pcp,adfernandes/pcp,mbaldessari/pcp,edwardt/pcp,tjanez/pcp,edwardt/pcp,edwardt/pcp,edwardt/pcp,andyvand/cygpcpfans,ryandoyle/pcp_original,mbaldessari/pcp,aeg-aeg/pcpfans,wuliming/pcp,prasincs/pcp,adfernandes/pcp,tjanez/pcp,ryandoyle/pcp_original,prasincs/pcp,tjanez/pcp,prasincs/pcp,ryandoyle/pcp_original,prasincs/pcp,tjanez/pcp,wuliming/pcp,aeg-aeg/pcpfans,andyvand/cygpcpfans,wuliming/pcp,aeg-aeg/pcpfans,andyvand/cygpcpfans,wuliming/pcp,aeg-aeg/pcpfans,andyvand/cygpcpfans,aeg-aeg/pcpfans,ryandoyle/pcp_original,andyvand/cygpcpfans,prasincs/pcp,aeg-aeg/pcpfans,mbaldessari/pcp,wuliming/pcp,adfernandes/pcp,mbaldessari/pcp,andyvand/cygpcpfans,andyvand/cygpcpfans,adfernandes/pcp,edwardt/pcp,adfernandes/pcp,prasincs/pcp,ryandoyle/pcp_original,edwardt/pcp,edwardt/pcp,adfernandes/pcp,wuliming/pcp,andyvand/cygpcpfans,adfernandes/pcp,tjanez/pcp