Deal with the possibility of negative available space from the file server to avoid Bad Things(TM) happening (eg: df crashing with a floating point exception).
Deal with the possibility of negative available space from the file server
to avoid Bad Things(TM) happening (eg: df crashing with a floating point
exception).

Submitted by:	Harold Gutch <logix@foobar.franken.de>
Approved by:	re (scottl)

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