Skip adding swap lines to /etc/fstab if swap is 0 sized

[allanjude]

Summary

Reported by: dim

[dim]

LGTM. But this is better reviewed by somebody who knows their way around bsdinstall. :)

[eadler]

this counts as mentor and src approval. Go ahead

[allanjude]

Fix syntax error found by Michael Dexter and Devin Teske

[dteske]

Let "sh -n filename" be your friend, my friend ;D

In this case, the output of "sh -n zfsboot" was spot-on:
zfsboot: 979: Syntax error: "else" unexpected (expecting "then")

The proposed revision fixes the problem and I approve of this revision (adding "; then"). Thanks Allan.

[allanjude]

Committed as rS283288