fix: better error handling in SendWork

[teslashibe]

Fix Nil Pointer Dereference in SendWork Function for #408

This closes #408

Description

This PR addresses a critical bug in the SendWork function within the workers.go file, where a nil pointer dereference panic occurs under certain conditions. The issue was identified in the remote worker spawning logic, specifically when the SpawnNamed method returns a nil PID *actor.PID, and subsequent operations attempt to use this nil pointer, leading to a runtime panic.

Changes

• Nil Check for spawnedPID: Added a nil check immediately after attempting to spawn a new actor with SpawnNamed. If spawnedPID is nil, the function logs an error and returns early from the goroutine, preventing the nil pointer dereference.
• Correct Loop Variable Capture: Modified the anonymous goroutine function within the loop to take the loop variable [p] as a parameter. This change ensures that each goroutine receives the correct instance of [p], avoiding potential issues with loop variable capture in goroutines.

Impact

• Reliability: This fix prevents the worker from crashing due to a nil pointer dereference, thus improving the overall reliability of the worker's operation.
• Error Handling: By adding proper error handling and logging, the system can now gracefully handle scenarios where remote actor spawning fails, allowing for better diagnosis and maintenance.
• Concurrency Safety: Correcting the loop variable capture in goroutines ensures that concurrent operations behave as expected, without unintended side effects.

[mudler]

Looking good! just few minor nits as in the other PRs, but nothing blocking.