Merge bitcoindevkit/bdk#619: Fix index out of bound error

d9b9b3dc464d6a9cd4157cc4135a2e7b88ce4ab3 Fix InvalidColumnIndex error (Philipp Hoenisch)

Pull request description:

  This query returns 7 rows, so last row is index 6

  ### Checklists

  #### All Submissions:

  * [x] I've signed all my commits
  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
  * [x] I ran `cargo fmt` and `cargo clippy` before committing

  #### Bugfixes:

  * [x] I've added tests to reproduce the issue which are now passing

ACKs for top commit:
  danielabrozzoni:
    tACK d9b9b3dc464d6a9cd4157cc4135a2e7b88ce4ab3
  rajarshimaitra:
    tACK d9b9b3dc464d6a9cd4157cc4135a2e7b88ce4ab3

Tree-SHA512: 8a3d8a291daa4af86a2a2eacc31f002972dd9cdb9bf300a4b09e2e015c4a967dc4fa7e925afbcce8b104a01e1d7f7c8cb0badda8e1ac5ade511681f490c719d5