[gtk-doc] gtkdoc-mkdb: fix some invalid docbook

[Stefan Kost <stefkost src gnome org>]

commit fe561f956028d593410ff2b37b3d825a33388cd5
Author: Stefan Sauer <ensonic users sf net>
Date:   Fri Apr 24 08:42:06 2015 +0200

    gtkdoc-mkdb: fix some invalid docbook

 gtkdoc-mkdb.in |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/gtkdoc-mkdb.in b/gtkdoc-mkdb.in
index 3372fed..fee5cbb 100755
--- a/gtkdoc-mkdb.in
+++ b/gtkdoc-mkdb.in
@@ -2547,6 +2547,9 @@ sub OutputSGMLFile {
         $object_anchors .= "<anchor id=\"$id\"$empty_element_end";
     }
 
+    # Make sure we produce valid docbook
+    $$functions_details ||= "<para />";
+
     # We used to output this, but is messes up our UpdateFileIfChanged code
     # since it changes every day (and it is only used in the man pages):
     # "<refentry id="$section_id" revision="$mday $month $year">"