Update xenforo.rb (#5622)

#Fix for the error: xenforo.rb: 160: in `gsub!': invalid byte sequence in UTF-8 (ArgumentError)

script/import_scripts/xenforo.rb

@@ -156,6 +156,12 @@ class ImportScripts::XenForo < ImportScripts::Base
     # phpBB shortens link text like this, which breaks our markdown processing:
     #   [http://answers.yahoo.com/question/index ... 223AAkkPli](http://answers.yahoo.com/question/index?qid=20070920134223AAkkPli)
     #
+    #Fix for the error: xenforo.rb: 160: in `gsub!': invalid byte sequence in UTF-8 (ArgumentError)
+    if ! s.valid_encoding?
+      s = s.encode("UTF-16be", invalid: :replace, replace: "?").encode('UTF-8')
+    end
+    #End Fix
+    
     # Work around it for now:
     s.gsub!(/\[http(s)?:\/\/(www\.)?/, '[')