_abbrev_table used a list comprehension inline inside a generator
expression filter. In Python 3, list comprehensions have their own
scope, so the loop variable 'cu' was not visible to the outer 'if'
condition — causing a NameError on every !h / !help DM command.
Extract the comprehension to a local variable 'cats_upper' so both
the iteration and the filter operate on the same pre-built list.