Traditional plugin reports error on re-initialize

During metric re-initialization (triggered by OA), the plugin reports:
```
Score-P x86_energy_sync plugin: [taurusi5241][2977185363346065][FATAL]: No metrics added. Check your metrics!
```
Still, energy is measured.

More information in `/lustre/ssd/p_readex/flexi/test/slurm-17120294.out` and  `/lustre/ssd/p_readex/flexi/test/run_psc_x86e_error_message.sh`