The default_mounts[i].destination is never NULL except in the last
'stop here' entry.  Coverity doesn't know about that and so is spewing
a warning.  In any case, let's add a more stringent check in case someone
accidentally adds a NULL there later.
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>