title: Detect incorrect pre-image length when submitting a referenda

doc:
  - audience: Runtime User
    description: |
      When submitting a referenda the `proposal` is passed as argument.
      The `proposal` is most of the time a reference to a `pre-image` and
      which also contains the length of the `pre-image`. This pull request
      adds some logic to check that if the `pre-image` already exists and if
      it exists, it ensures that the length is passed correctly. This prevents
      that the referenda can not be executed because of a mismatch of this
      length.

crates:
  - name: pallet-referenda