SystemTools: Fix GetOperatingSystemNameAndVersion empty string return

Dženan Zukićrequested to merge
dzenanz/kwsys:master into master

Avoid undefined behavior caused by constructing std::string from 0.

Issue: https://github.com/InsightSoftwareConsortium/ITK/issues/2637
Topic-rename: SystemTools-return-string

Edited by Brad King

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