Fix EZP-20505: IO Exception when file isn't found

https://jira.ez.no/browse/EZP-20502.

Catches the NotFound exceptions returned by the IO handlers when a file is referenced in the database but doesn't exist in storage, and logs errors instead. This is done in the various FieldTypes that use the IO Service, meaning the the IO handlers themselves will keep throwing exceptions, as a missing file *is* an exception from their perspective.

It should degrade correctly,and shouldn't affect development anymore.

## TODO
- [x] Do the same changes to BinaryBase, if applicable