WinXP Compatibility for PdhUtil#PdhLookupPerfNameByIndex

[dbwiddis]

While the fix in #1052 worked on one XP system it did not work on another. Not sure if it was character encoding or bitness or something else, but the docs were also unclear as to the behavior of the buffer length value:

The function sets pcchNameBufferSize to either the required size or the size of the buffer that was used.

And also suggesting error code response varied:

PDH_INVALID_ARGUMENT ... on some releases you could receive this error if the specified size on input is greater than zero but less than the required size.

This second fix should work and passes tests on a few different XP VMs. Vista+ does the "pass null, get size, get result" calls. For XP the buffer is incremented until it succeeds so we don't have to rely on the returned size.

[matthiasblaesing]

Thank you. Looks sane - I'll give it night to settle though.