Core/Movement: Typo fix for falling to void case (#18611)

src/server/game/Handlers/MovementHandler.cpp

@@ -426,7 +426,7 @@ void WorldSession::HandleMovementOpcodes(WorldPacket& recvPacket)
                     // player can be alive if GM/etc
                     // change the death state to CORPSE to prevent the death timer from
                     // starting in the next player update
-                    if (!plrMover->IsAlive())
+                    if (plrMover->IsAlive())
                         plrMover->KillPlayer();
                 }
             }