[FIX] Category: Load the category dump lazy

The script test failed, because it always told it loaded the
category dump (if the file existed). This loads the category dump
only as soon as it's used. Because that instance is now also storing
the filename it's possible to dump it into the same file without
determining the filename.

Change-Id: Ia3aa847afd18d21a5ae85e5c2647178ef29fba4a
Merge "[FIX] Category: Load the category dump lazy"