Consume the entire enumerator before letting it go out of scope

[driehuis]

This diff seems to fix issue #614. I have replaced blnsvr.exe with a version that contains this patch, and the events are gone. I tested that blnsvr.exe built without this patch does exhibit the behavior. The service is running without any visible issues, but I have not been able to do a meaningful test of its functionality.

I compared the usage of IWbemServices:ExecQuery in memstat.cpp with other C++ code that uses the same API. The only material difference I noticed was that the other code used the form

    while(1) {
        hres = pEnumerator->Next(WBEM_INFINITE, 1, &pclsObj, &uReturn);
        if(0 == uReturn) {
            break;
        }
    }

which guarantees that the enumerator is consumed in its entirety. Apparently, the API doesn't clean up its own context unless all items are consumed and throws a hissy fit later on, and quite likely only on a few of the calls.

Please review the patch carefully. I think I got the indentation right according to the "When in Rome" rule, but I'm not positive. The patch is paranoid; the check for enumerator==NULL can probably be eliminated, and it could be made shorter.

I did not run the test suite.

[YanVugenfirer]

Keeping the PR as a reminder