Chunnel: Add a ground veh flag for (maybe) being in a chunnel

Use this to avoid inclination change code in non-chunnel wormholes.

src/ground_vehicle.hpp

@@ -16,6 +16,7 @@
 #include "vehicle_gui.h"
 #include "landscape.h"
 #include "window_func.h"
+#include "tunnel_map.h"
 #include "widgets/vehicle_widget.h"
 
 /** What is the status of our acceleration? */
@@ -54,6 +55,7 @@ enum GroundVehicleFlags {
 	GVF_GOINGUP_BIT              = 0,  ///< Vehicle is currently going uphill. (Cached track information for acceleration)
 	GVF_GOINGDOWN_BIT            = 1,  ///< Vehicle is currently going downhill. (Cached track information for acceleration)
 	GVF_SUPPRESS_IMPLICIT_ORDERS = 2,  ///< Disable insertion and removal of automatic orders until the vehicle completes the real order.
+	GVF_CHUNNEL_BIT              = 3,  ///< Vehicle may currently be in a chunnel. (Cached track information for inclination changes)
 };
 
 /**
@@ -225,6 +227,10 @@ struct GroundVehicle : public SpecializedVehicle<T, Type> {
 			this->z_pos += HasBit(this->gv_flags, GVF_GOINGUP_BIT) ? d : -d;
 		}
 
+		if (HasBit(this->gv_flags, GVF_CHUNNEL_BIT) && !IsTunnelTile(this->tile)) {
+			ClrBit(this->gv_flags, GVF_CHUNNEL_BIT);
+		}
+
 		assert(this->z_pos == GetSlopePixelZ(this->x_pos, this->y_pos));
 	}
 
@@ -241,7 +247,7 @@ struct GroundVehicle : public SpecializedVehicle<T, Type> {
 		int old_z = this->z_pos;
 
 		if (in_wormhole) {
-			this->UpdateZPositionInWormhole();
+			if (HasBit(this->gv_flags, GVF_CHUNNEL_BIT)) this->UpdateZPositionInWormhole();
 		} else if (new_tile) {
 			this->UpdateZPositionAndInclination();
 		} else {

src/tunnelbridge_cmd.cpp

@@ -2108,6 +2108,7 @@ static VehicleEnterTileStatus VehicleEnter_TunnelBridge(Vehicle *v, TileIndex ti
 				if (frame == _tunnel_visibility_frame[dir]) {
 					t->tile = tile;
 					t->track = TRACK_BIT_WORMHOLE;
+					if (Tunnel::GetByTile(tile)->is_chunnel) SetBit(t->gv_flags, GVF_CHUNNEL_BIT);
 					t->vehstatus |= VS_HIDDEN;
 					return VETSB_ENTERED_WORMHOLE;
 				}
@@ -2133,6 +2134,7 @@ static VehicleEnterTileStatus VehicleEnter_TunnelBridge(Vehicle *v, TileIndex ti
 					rv->tile = tile;
 					rv->cur_image_valid_dir = INVALID_DIR;
 					rv->state = RVSB_WORMHOLE;
+					if (Tunnel::GetByTile(tile)->is_chunnel) SetBit(rv->gv_flags, GVF_CHUNNEL_BIT);
 					rv->vehstatus |= VS_HIDDEN;
 					return VETSB_ENTERED_WORMHOLE;
 				} else {