Predicates where {fieldname}.length is used need the fieldname namespace/tablename in path to avoid ambiguous field name problem when query is sent of sqllite layer about encrypted-core-data

[gavin-black]

@oliverwoolgar thank you very much for the fix description, and taking the time to figure out the issue. If you have a pull request feel free to submit it, and I can go ahead an integrate it.

[zerpt]

@oliverwoolgar We incorporated your fix, which seems to work for most simple cases. I believe this might fail on deep relationship chain predicate operands, but we'll cross that bridge when the issue is confirmed and raised.

Thanks for the info and your help!