Prevent crash in agent_proxmox_ve special agent when backup log fetch fails

[Eulex0x]

Summary:

The agent_proxmox_ve special agent was crashing whenever backup logs were fetched via fetch_backup_data() due to unhandled errors, causing the entire agent to fail. To fix this, I wrapped the fetch_backup_data() call in a try/except block. Now, if an error occurs (such as API failures or data inconsistencies), the agent logs a warning and continues gracefully by using an empty result for backup logs instead of crashing. This change improves the overall stability and reliability of the agent, ensuring that it still provides other monitoring data even if some backup log retrievals fail. Additionally, the internal logic processes backup logs per VM, so individual VM failures do not affect the entire data set.

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