Fix issue preventing build in Windows

[mvadu]

Removed nil in line#13 return which was stopping the build in Windows. src\github.com\influxdb\influxdb\tsdb\engine\tsm1\mmap_windows.go:13: too many arguments to return issue is fixed.

It will fix #4358 but will not let tsm1 to run on Windows. At least users can test other improvements and bug fixes from 0.9.6

[jwilder]

@mvadu There is a PR that should allow windows to work, but the tests fail on windows. #5039

[mvadu]

@jwilder Yup, I myself implemented the mmap logic in #4981 (which is used as is in #5039), but it will alone won't make tsm work as rename while file is in use is not liked by Windows.

[jwilder]

@mvadu Have you tried with latest? 99c313d fixed a file leak which might have prevented the rename. If it still occurs, then we can re-work how the renaming works. The files should be closed while the rename runs though.

[mvadu]

@jwilder Yes, I just posted an update there with latest head from master branch, with my changes. Please check #4981

[mvadu]

Closed in #4981