Fix link title only if it has markup

Author: kristijanhusak

scripts/pandoc_fix_links.lua

@@ -7,16 +7,20 @@ function Link(el)
   el.target = target
 
   local content = {}
+  local has_markup = false
   for _, item in ipairs(el.content) do
     if item.text then
       table.insert(content, item.text)
     end
     if item.content then
+      has_markup = true
       for _, subitem in ipairs(item.content) do
         table.insert(content, subitem.text)
       end
     end
   end
-  el.content = table.concat(content, '_')
+  if has_markup then
+    el.content = table.concat(content, '_')
+  end
   return el
 end