1. Move the declaration of const vshCmdDef *help - it should be at the
top of the "if" rather than in the middle.
2. Change a comparison from && to || - without doing so we could crash
on commands like 'virsh list' which would allow completion of some
non -- option based on whatever was found in the current working
directory and then as soon as that was completed, the next <tab>
would crash since "opt" would be returned as NULL, but the check
was dereferencing "&& opt->type"
3. Before dereferencing opt->completer, be sure opt isn't NULL.