Merge pull request #505 from DahBlount/Fix-for-Coverity-#1343617

Fix for coverity 1343617

Author: niffiwan

code/ai/aiturret.cpp

@@ -1343,6 +1343,7 @@ void ship_get_global_turret_gun_info(object *objp, ship_subsys *ssp, vec3d *gpos
 		model_instance_find_world_point(&tmp_pos, &avg, tp->model_num, Ships[objp->instance].model_instance_num, tp->turret_gun_sobj, &objp->orient, &objp->pos);
 
 		if (targetp == nullptr) {
+			Assertion(ssp->turret_enemy_objnum >= 0, "The turret enemy object number %d for %s on ship number %d is invalid.", ssp->turret_enemy_objnum, ssp->sub_name, ssp->parent_objnum);
 			object *lep = &Objects[ssp->turret_enemy_objnum];
 
 			int best_weapon_tidx = turret_select_best_weapon(ssp, lep);
@@ -1356,10 +1357,8 @@ void ship_get_global_turret_gun_info(object *objp, ship_subsys *ssp, vec3d *gpos
 			float weapon_system_strength = ship_get_subsystem_strength(&Ships[ssp->parent_objnum], SUBSYSTEM_WEAPONS);
 
 			if ((ssp->targeted_subsys != nullptr) && !(ssp->flags & SSF_NO_SS_TARGETING)) {
-				if (ssp->turret_enemy_objnum != -1) {
-					vm_vec_unrotate(&enemy_point, &ssp->targeted_subsys->system_info->pnt, &Objects[ssp->turret_enemy_objnum].orient);
-					vm_vec_add2(&enemy_point, &ssp->last_aim_enemy_pos);
-				}
+				vm_vec_unrotate(&enemy_point, &ssp->targeted_subsys->system_info->pnt, &Objects[ssp->turret_enemy_objnum].orient);
+				vm_vec_add2(&enemy_point, &ssp->last_aim_enemy_pos);
 			} else {
 				if ((lep->type == OBJ_SHIP) && (Ship_info[Ships[lep->instance].ship_info_index].flags & (SIF_BIG_SHIP | SIF_HUGE_SHIP))) {
 					ai_big_pick_attack_point_turret(lep, ssp, &tmp_pos, &tp->turret_norm, &enemy_point, tp->turret_fov, MIN(wip->max_speed * wip->lifetime, wip->weapon_range));