test: bad rx-state after cleanup

[enrico-teterra-maramalabs]

This PR contains:

a failing test

Describe the problem you have without this PR

to reproduce the issue:

• have an rx-state
• make more than 5 writes to ensure _cleanup does its thing
• the state has an additional "" property which causes problems further down the line

[pubkey]

Can you make the test by only using the "normal" RxDB api without accessing the internal storageInstance?
Atm this test does not seem to match you reproduction steps.

[enrico-teterra-maramalabs]

yep no problem, please take a look at the test now

the test as it is now fails with:

+ expected - actual

       {
      -  "": {
      -    "foo": "bar6"
      -  }
         "foo": "bar6"
       }