Fix multi-thread issue when monsters cast against players that left (#3491)
Fix multi-thread issue when monsters cast against players that left (#3491)

Scenario:

Monster targets player
Monster begins to cast a spell at player (windup)
Player teleports out
Monster windup completes and casts
TryResit code now accesses two threads at once determining if the spell can be landed on the player that's now gone.
LtRipley36706/ACE,LtRipley36706/ACE,ACEmulator/ACE,ACEmulator/ACE,ACEmulator/ACE,LtRipley36706/ACE