Division by zero in `send_conversion_efficiencies`

[Flix6x]

Traceback (most recent call last):
  File "/usr/local/lib/python3.13/site-packages/flexmeasures_client/s2/control_types/FRBC/frbc_tunes.py", line 355, in send_conversion_efficiencies
    100
    ~~~
    * thp_op_mode_element.fill_rate.end_of_range
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    / thp_op_mode_element.power_ranges[0].end_of_range
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
ZeroDivisionError: float division by zero