contrib/lisp/org-e-texinfo.el: Fix export bugs
* contrib/lisp/org-e-texinfo.el (org-e-texinfo--generate-detailed): Do
not run if there are no headlines in the file.
(org-e-texinfo-template): Generate menu and detailed menu in initial
let form. Only insert them if non-empty.
(org-e-texinfo-headline): Ensure that %'s are properly escaped in
@node's to prevent parse errors.
(org-e-texinfo-make-menu): Do not insert "detailed" if menu is empty,
return empty entry instead.
Thanks to Bastien for reporting the failures with headline-less files
and simple "%" in the headline.