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.

contrib/lisp/org-e-texinfo.el

@@ -529,6 +529,7 @@ recurse into all children as well."
 MENU is the parse-tree to work with.  LEVEL is the starting level
 for the menu headlines and from which recursion occurs.  INFO is
 a plist containing contextual information."
+  (when level
     (let ((max-depth (plist-get info :headline-levels)))
       (when (> max-depth level)
 	(loop for headline in menu append
@@ -546,7 +547,7 @@ a plist containing contextual information."
 		     ;; Start the process over the next level down.
 		     (recursion (org-e-texinfo--generate-detailed sublist (1+ level) info)))
 		(setq recursion (append submenu recursion))
-	      recursion)))))
+		recursion))))))
 
 (defun org-e-texinfo--generate-menu-list (tree level info)
   "Generate the list of headlines that are within a given level
@@ -656,7 +657,9 @@ holding export options."
 	 (dirdesc (plist-get info :texinfo-dirdesc))
 	 ;; Spacing to align description (column 32 - 3 for `* ' and
 	 ;; `.' in text.
-	 (dirspacing (- 29 (length dirtitle))))
+	 (dirspacing (- 29 (length dirtitle)))
+	 (menu (org-e-texinfo-make-menu info 'main))
+	 (detail-menu (org-e-texinfo-make-menu info 'detailed)))
     (concat
      ;; Header
      header "\n"
@@ -721,17 +724,20 @@ holding export options."
      "@insertcopying\n"
      "@end ifnottex\n\n"
 
+     ;; Do not output menus if they are empty
+     (if menu
 	 ;; Menu
-     "@menu\n"
+	 (concat "@menu\n"
-     (org-e-texinfo-make-menu info 'main)
+		 menu
 		 "\n\n"
 		 ;; Detailed Menu
-     "@detailmenu\n"
+		 (if detail-menu
+		     (concat "@detailmenu\n"
 			     " --- The Detailed Node Listing ---\n"
-     (org-e-texinfo-make-menu info 'detailed)
+			     detail-menu
 			     "\n\n"
-     "@end detailmenu\n"
+			     "@end detailmenu\n"))
-     "@end menu\n"
+		   "@end menu\n"))
      "\n\n"
 
      ;; Document's body.
@@ -902,8 +908,9 @@ holding contextual information."
 	 (index (org-element-property :index headline))
 	 ;; Create node info, to insert it before section formatting.
 	 (node (format "@node %s\n"
-		       (org-export-data
+		       (replace-regexp-in-string
-			(org-element-property :title headline) info)))
+			"%" "%%"
+			(org-export-data (org-element-property :title headline) info))))
 	 ;; Menus must be generated with first child, otherwise they
 	 ;; will not nest properly
 	 (menu (let* ((first (org-export-first-sibling-p headline info))
@@ -1254,8 +1261,7 @@ are generated directly."
      ((eq level 'detailed)
       ;; Requires recursion
       ;;(org-e-texinfo--build-detailed-menu parse top info)
-      (or (org-e-texinfo--build-menu parse top info 'detailed)
+      (org-e-texinfo--build-menu parse top info 'detailed))
-	  "detailed"))
      ;; Otherwise do nothing
      (t))))