rsvp format: fix valid() to avoid segfaults

... on "hashes" that don't even have the format tag, e.g. 1acbed4a27b-20da3
pkzip format: Mute warning about missing files if we're just reading pot lines.
Remove some #ifdef DEBUG, or change them to something more specific like
POTSYNC_DEBUG or DYNA_SALT_DEBUG.
Max length fixes in rules.c for internal encoding.
Fix handling of invalid UTF-8 in mssql05. Closes #830
Ensure key cleaning on invalid UTF-8 in same fast formats. No
problem seen with these but #830 hinted we might get problems
so we play safe.
mask mode now supports --max-length