ox-rss: Prevent dropping lower level headlines

* contrib/lisp/ox-rss.el (org-rss-headline): Transcode lower level
  headlines (headlines with level > 1) using the html backend.  Do not
  drop them.

Previously, lower level headlines were dropped and did not appear in the
exported RSS output.

contrib/lisp/ox-rss.el

@@ -226,59 +226,59 @@ Return output file name."
   "Transcode HEADLINE element into RSS format.
 CONTENTS is the headline contents.  INFO is a plist used as a
 communication channel."
-  (unless (or (org-element-property :footnote-section-p headline)
-	      ;; Only consider first-level headlines
-	      (> (org-export-get-relative-level headline info) 1))
-    (let* ((author (and (plist-get info :with-author)
-			(let ((auth (plist-get info :author)))
-			  (and auth (org-export-data auth info)))))
-	   (htmlext (plist-get info :html-extension))
-	   (hl-number (org-export-get-headline-number headline info))
-	   (hl-home (file-name-as-directory (plist-get info :html-link-home)))
-	   (hl-pdir (plist-get info :publishing-directory))
-	   (hl-perm (org-element-property :RSS_PERMALINK headline))
-	   (anchor (org-export-get-reference headline info))
-	   (category (org-rss-plain-text
-		      (or (org-element-property :CATEGORY headline) "") info))
-	   (pubdate0 (org-element-property :PUBDATE headline))
-	   (pubdate (let ((system-time-locale "C"))
-		      (if pubdate0
-			  (format-time-string
-			   "%a, %d %b %Y %H:%M:%S %z"
-			   (org-time-string-to-time pubdate0)))))
-	   (title (or (org-element-property :RSS_TITLE headline)
-		      (replace-regexp-in-string
-		       org-bracket-link-regexp
-		       (lambda (m) (or (match-string 3 m)
-				  (match-string 1 m)))
-		       (org-element-property :raw-value headline))))
-	   (publink
-	    (or (and hl-perm (concat (or hl-home hl-pdir) hl-perm))
-		(concat
-		 (or hl-home hl-pdir)
-		 (file-name-nondirectory
-		  (file-name-sans-extension
-		   (plist-get info :input-file))) "." htmlext "#" anchor)))
-	   (guid (if org-rss-use-entry-url-as-guid
-		     publink
-		   (org-rss-plain-text
-		    (or (org-element-property :ID headline)
-			(org-element-property :CUSTOM_ID headline)
-			publink)
-		    info))))
-      (if (not pubdate0) "" ;; Skip entries with no PUBDATE prop
-	(format
-	 (concat
-	  "<item>\n"
-	  "<title>%s</title>\n"
-	  "<link>%s</link>\n"
-	  "<author>%s</author>\n"
-	  "<guid isPermaLink=\"false\">%s</guid>\n"
-	  "<pubDate>%s</pubDate>\n"
-	  (org-rss-build-categories headline info) "\n"
-	  "<description><![CDATA[%s]]></description>\n"
-	  "</item>\n")
-	 title publink author guid pubdate contents)))))
+  (if (> (org-export-get-relative-level headline info) 1)
+      (org-export-data-with-backend headline 'html info)
+    (unless (org-element-property :footnote-section-p headline)
+      (let* ((author (and (plist-get info :with-author)
+			  (let ((auth (plist-get info :author)))
+			    (and auth (org-export-data auth info)))))
+	     (htmlext (plist-get info :html-extension))
+	     (hl-number (org-export-get-headline-number headline info))
+	     (hl-home (file-name-as-directory (plist-get info :html-link-home)))
+	     (hl-pdir (plist-get info :publishing-directory))
+	     (hl-perm (org-element-property :RSS_PERMALINK headline))
+	     (anchor (org-export-get-reference headline info))
+	     (category (org-rss-plain-text
+			(or (org-element-property :CATEGORY headline) "") info))
+	     (pubdate0 (org-element-property :PUBDATE headline))
+	     (pubdate (let ((system-time-locale "C"))
+			(if pubdate0
+			    (format-time-string
+			     "%a, %d %b %Y %H:%M:%S %z"
+			     (org-time-string-to-time pubdate0)))))
+	     (title (or (org-element-property :RSS_TITLE headline)
+			(replace-regexp-in-string
+			 org-bracket-link-regexp
+			 (lambda (m) (or (match-string 3 m)
+					 (match-string 1 m)))
+			 (org-element-property :raw-value headline))))
+	     (publink
+	      (or (and hl-perm (concat (or hl-home hl-pdir) hl-perm))
+		  (concat
+		   (or hl-home hl-pdir)
+		   (file-name-nondirectory
+		    (file-name-sans-extension
+		     (plist-get info :input-file))) "." htmlext "#" anchor)))
+	     (guid (if org-rss-use-entry-url-as-guid
+		       publink
+		     (org-rss-plain-text
+		      (or (org-element-property :ID headline)
+			  (org-element-property :CUSTOM_ID headline)
+			  publink)
+		      info))))
+	(if (not pubdate0) "" ;; Skip entries with no PUBDATE prop
+	  (format
+	   (concat
+	    "<item>\n"
+	    "<title>%s</title>\n"
+	    "<link>%s</link>\n"
+	    "<author>%s</author>\n"
+	    "<guid isPermaLink=\"false\">%s</guid>\n"
+	    "<pubDate>%s</pubDate>\n"
+	    (org-rss-build-categories headline info) "\n"
+	    "<description><![CDATA[%s]]></description>\n"
+	    "</item>\n")
+	   title publink author guid pubdate contents))))))
 
 (defun org-rss-build-categories (headline info)
   "Build categories for the RSS item."