Fix some more int-to-enum conversion complaint.

While we're at it, log a message if a Lua file format module lacks a
read or a seek-read routine, rather than completely silently ignoring
that module if it claims a file.

Change-Id: I9778f7835922439e2d3708614689280ef7b61d33
Reviewed-on: https://code.wireshark.org/review/4590
Reviewed-by: Guy Harris <guy@alum.mit.edu>