Show empty dropdown menu when no app uses dGPU

[GroobleDierne]

Current dropdown menu when there is no application using the discrete GPU:

This is caused by the strange nvidia-smi output when nothing is running:

~$ nvidia-smi pmon --id 0:01:00.0 --count 1
# gpu         pid   type     sm    mem    enc    dec    jpg    ofa    command 
# Idx           #    C/G      %      %      %      %      %      %    name 
    0          -     -      -      -      -      -      -      -    -