Memory leak on windows

[xianglin1998]

After my test, if function is implement from WMI, the all logic will memory leak after Get

VARIANT type need correct Clear

Read doc from Microsoft, we can get correct fixed. Release function is VariantClear.

https://learn.microsoft.com/en-us/windows/win32/api/wbemcli/nf-wbemcli-iwbemclassobject-get

(BTW: Indeed very few people running commercial databases on Windows.)

[neel5481]

Thank you @xianglin1998 WIP PR ( #22 )

[xianglin1998]

Thank you.