Fix filters with intermediate null tag values

[tyrasd]

SQL has some "unexpected" behaviour when it comes to handling NULL values, for example the = ANY array comparison results in null if the value it operates on is NULL (instead of false).

If the left-hand expression yields null, the result of ANY is ordinarily null

And when this is combined with the boolean NOT operator, this results in cases where one would expect a true-thy value, but gets NULL instead.

For example, a filter like amenity=bench and NOT (foo in (bar)) will not return features with amenity=bench and no foo tag.

This PR hardens the filter statements which can have intermediate NULL values to include extra is not null checks such that the filters can also be used together with a NOT negation.

TODO:

• some tests now result in odd assert [<Record count=3936621437>] == [<Record count=765879661>] – not sure what's going on there...