Tidy code.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Avoid passing undef as a character string.

For some reason (probably a bug in Pod::SAX), we get passed undef as the
character string to the characters method of PodSAXToTextMarkup.  This
causes copious warnings further down the stack, so simply ignore this
event if it occurs.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>