fix #12183: correct erroneous bitsize

This PR is most easily tested with a local server.

When you create a fresh database with,
```
psql -U omero omero <OMERO5.0__0.sql
```
or suchlike then if the `OMERO5.0__0.sql` file predates this PR then you will find in your database that,
```
select value, bitsize from pixelstype order by id;
```
has a 32-bit `uint16`.

With this PR, you should find that starting the server corrects this database entry and,
```
grep DBUInt16Check dist/var/log/Blitz-0.log
```
notes that this happened. Subsequent server restarts will not log a further update message. Also, a new,
```
bin/omero db script
```
will generate a `OMERO5.0__0.sql` that creates a correct database so that starting the server with a database generated from this new file also will not log a further update message.

--rebased-from #2308 in a manner so as to fix http://trac.openmicroscopy.org.uk/ome/ticket/12183.