Async queue destruction

[ChrisspyB]

This is likely an error on the C/C++ side of FDB, rather than pyfdb.

Running the snippet

import pyfdb
fdb1 = pyfdb.FDB()
data = open(tests_dir / "x138-300.grib", "rb").read()
fdb1.archive(data)
fdb1.flush()
list_output = next(fdb1.list(keys=True))

throws the error

SeriousBug: Destructing incomplete async queue in (fdb5/src/fdb5/api/helpers/APIIterator.h:141 ~APIAsyncIterator).

It is likely that the destruction of the fdb object should first close the queue created by fdb.list, but isn't doing so. Or something along those lines.