Remove empty modules in postProcess
Imported from http://bugzilla.roxen.com/bugzilla/show_bug.cgi?id=1956
Reported by Martin Nilsson, IDA nilsson@pike.ida.liu.se
After handleAppears has been run there will be some empty modules, e.g. _Image, in the XML file. These should be cleared out so they doesn't interfere with layouting.