Prevent projectiles from crashing server when removed when it punched something (wither skull hitting the wither will cause this), mark wither skull with _removed = true when death timer removes it

mods/ENTITIES/mobs_mc/wither.lua

@@ -201,6 +201,7 @@ mcl_mobs.register_mob("mobs_mc:wither", {
 					self._death_timer = self._death_timer + self.health - self._health_old
 					if self.health == self._health_old then self._death_timer = self._death_timer + dtime end
 					if self._death_timer > 100 then
+						self._removed = true
 						self.object:remove()
 						return false
 					end

mods/ITEMS/vl_projectile/init.lua

@@ -276,6 +276,9 @@ local function handle_entity_collision(self, entity_def, projectile_def, object)
 	if do_damage then
 		object:punch(self.object, 1.0, projectile_def.tool or { full_punch_interval = 1.0, damage_groups = dmg }, dir )
 
+		-- Guard against crashes when projectiles get destroyed in response to what it punched
+		if not self.object:get_pos() then return true end
+
 		-- Indicate damage
 		damage_particles(vector.add(pos, vector.multiply(self.object:get_velocity(), 0.1)), self._is_critical)