Improve doxygen slightly

Signed-off-by: Adam C. Emerson <aemerson@linuxbox.com>
Remove another NULL pointer error check

These really should all get taken out since they're obvious programming
faults and should do something catastrophic, not just get logged
somewhere.

Signed-off-by: Adam C. Emerson <aemerson@linuxbox.com>
Another doxygen fix

Actually make the grouping braces valid doxygen comments.

Signed-off-by: Adam C. Emerson <aemerson@linuxbox.com>