Manual testing - index out of range error in candlesticktester

In the manual test candlesticktester, an "index out of range" assertion error happens which results in a crash. This happens when trying to detach the model mapper after it has been attached.

Steps to reproduce:

1. Left-click "Detach model mapper" before having left-clicked "Attach model mapper". Notice that nothing happens,
2. Left-click "Attach model mapper".
3. Left-click "Detach model mapper". Notice that the "index out of range" error occurs, which will result in a crash

Expected behavior:

Left-clicking "Detach model mapper" should detach the model mapper.

Observed behavior:

Left-clicking "Detach model mapper" will result in a crash if done after having left-clicked "Attach model mapper".