virutil: Resolve Coverity RESOURCE_LEAK
virutil: Resolve Coverity RESOURCE_LEAK

This ends up being a very bizarre false positive. With an assist from
eblake, the claim is that mgetgroups() could return a -1 value, but yet
still have a groups buffer allocated, yet the example shown doesn't
seem to prove that.

Rather than fret about it, by adding a well placed sa_assert() on the
returned *list value we can "assure" ourselves that the mgetgroups()
failure path won't signal this condition.

Signed-off-by: John Ferlan <87558058f6f829e5ec976c8ef960720af4ff9c7d@redhat.com>

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