[Bug] Exception when reindexing trashed file.

[mistermult]

I'm implementing a new store that does not support deletions but this also works with the static store.

1. Index the store with some files.
2. Trash the files in the Web interface.
3. Press 'Index' to reindex the bags in the store.
   The 'Index' task is not succefull, because the trashed bag is still in the Database.

Traceback (most recent call last):
  File "#######/rbb_core/rbb_server/src/rbb_server/controllers/bag_controller.py", line 491, in put_bag_meta
    session.commit()
  File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/orm/scoping.py", line 162, in do
    return getattr(self.registry(), name)(*args, **kwargs)
  File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/orm/session.py", line 1027, in commit
    self.transaction.commit()
  File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/orm/session.py", line 494, in commit
    self._prepare_impl()
  File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/orm/session.py", line 473, in _prepare_impl
    self.session.flush()
  File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/orm/session.py", line 2459, in flush
    self._flush(objects)
  File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/orm/session.py", line 2597, in _flush
    transaction.rollback(_capture_exception=True)
  File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/util/langhelpers.py", line 68, in __exit__
    compat.reraise(exc_type, exc_value, exc_tb)
  File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/util/compat.py", line 153, in reraise
    raise value
  File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/orm/session.py", line 2557, in _flush
    flush_context.execute()
  File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/orm/unitofwork.py", line 422, in execute
    rec.execute(self)
  File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/orm/unitofwork.py", line 589, in execute
    uow,
  File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/orm/persistence.py", line 236, in save_obj
    update,
  File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/orm/persistence.py", line 996, in _emit_update_statements
    statement, multiparams
  File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/engine/base.py", line 988, in execute
    return meth(self, multiparams, params)
  File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/sql/elements.py", line 287, in _execute_on_connection
    return connection._execute_clauseelement(self, multiparams, params)
  File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/engine/base.py", line 1107, in _execute_clauseelement
    distilled_params,
  File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/engine/base.py", line 1253, in _execute_context
    e, statement, parameters, cursor, context
  File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/engine/base.py", line 1473, in _handle_dbapi_exception
    util.raise_from_cause(sqlalchemy_exception, exc_info)
  File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/util/compat.py", line 398, in raise_from_cause
    reraise(type(exception), exception, tb=exc_tb, cause=cause)
  File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/util/compat.py", line 152, in reraise
    raise value.with_traceback(tb)
  File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/engine/base.py", line 1249, in _execute_context
    cursor, statement, parameters, context
  File "/usr/local/lib/python3.5/dist-packages/sqlalchemy/engine/default.py", line 552, in do_execute
    cursor.execute(statement, parameters)
sqlalchemy.exc.IntegrityError: (psycopg2.errors.NotNullViolation) null value in column "in_trash" violates not-null constraint
DETAIL:  Failing row contains (1, 4, {"name": "abc.bag", "link": "abc.bag"}, abc.bag, f, null, f, 2019-09-08 14:43:05.849307, f, 0, null, null, null, null, ).

The value in in_trash is null because it is not set when reindexing the same file.