QueryParser Driver: Protect against NULLs

QueryParser Driver: Protect against NULLs

mrd.attrs->'value' can return NULL. If this happens:

Checking that the value is within a range or list will work fine.
NEGATING that will not.

This is because:
AND NULL returns NULL
AND NOT (NULL) also returns NULL

The solution? Adjust things so we can wrap all the offending checks in a
COALESCE to false. Then if mrd.attrs->'value' is null we get a false.

In the process we move any and all negations to outside the COALESCE.

Also apply the same logic to the bib_source filter, not to mention
making it support being negated.

Signed-off-by: Thomas Berezansky <tsbere@mvlc.org>
Signed-off-by: Dan Scott <dscott@laurentian.ca>