swars: When loading a level, restore tank turret angle

The turret angle should be set from transformation matrix,
like for all vehicles. This updates the old code which probably
was supposed to do that, but had some copy-paste errors.

Author: mefistotelis

src/lvfiles.c

@@ -258,15 +258,26 @@ ulong load_level_pc_handle(TbFileHandle lev_fh)
                 p_thing->U.UVehicle.Object = next_object - 1;
                 game_objects[next_object - 1].ThingNo = k;
                 VNAV_unkn_func_207(p_thing);
-                k = p_thing->U.UVehicle.MatrixIndex;
-                angle = LbArcTanAngle(local_mats[k].R[0][2], local_mats[k].R[2][2]);
-                p_thing->U.UVehicle.AngleY = (angle + LbFPMath_PI) & LbFPMath_AngleMask;
+                {
+                    k = p_thing->U.UVehicle.MatrixIndex;
+                    angle = LbArcTanAngle(local_mats[k].R[0][2], local_mats[k].R[2][2]);
+                    p_thing->U.UVehicle.AngleY = (angle + LbFPMath_PI) & LbFPMath_AngleMask;
+                }
 
                 veh_add(p_thing, p_thing->StartFrame);
-                k = p_thing->U.UVehicle.MatrixIndex;
-                angle = LbArcTanAngle(local_mats[k].R[0][2], local_mats[k].R[2][2]);
-                p_thing->U.UVehicle.AngleY = (angle + LbFPMath_PI) & LbFPMath_AngleMask;
-                if (p_thing->SubType == SubTT_VEH_MECH)
+
+                if (p_thing->SubType == SubTT_VEH_TANK)
+                {
+                    if (p_thing->U.UVehicle.SubThing != 0)
+                    {
+                        struct Thing *p_mgun;
+                        p_mgun = &things[p_thing->U.UVehicle.SubThing];
+                        k = p_mgun->U.UVehicle.MatrixIndex;
+                        angle = LbArcTanAngle(local_mats[k].R[0][2], local_mats[k].R[2][2]);
+                        p_mgun->U.UVehicle.AngleY = (angle + LbFPMath_PI) & LbFPMath_AngleMask;
+                    }
+                }
+                else if (p_thing->SubType == SubTT_VEH_MECH)
                 {
                     if (!mech_initialized)
                     {