Differenciate unset `content` from empty string
Differenciate unset `content` from empty string

`content` is an empty string when no description is given, but empty
string is falsy, thus resulting in the annotation not being displayed.

Refs: SassDoc/sassdoc#383

SassDoc/sassdoc-theme-default,zeidlos/sassdoc-theme-default,tf/sassdoc-theme-pageflow