genie_python (RIKENFE): workaround for not being able to load PV CS:INSTLIST

[zsoltkebel]

Adapt the code so it does not fail if this PV is inaccessible as genie python can be loaded in without it.

This is a temporary fix and useful improvement to genie python code. Ticket for root cause fixing: #8099

[zsoltkebel]

Added to hotfix page.

PR

• https://github.com/ISISComputingGroup/genie_python/pull/393