Chunnel patch 28396: Codechange: Chunnel portal must have minimal length of 4 tiles.

https://www.tt-forums.net/viewtopic.php?p=1183416#p1183416

src/terraform_cmd.cpp

@@ -270,7 +270,7 @@ CommandCost CmdTerraformLand(TileIndex tile, DoCommandFlag flags, uint32 p1, uin
 					}
 				}
 				/* Check if tunnel would take damage */
-				if (direction == -1 && IsTunnelInWay(tile, z_min)) {
+				if (direction == -1 && IsTunnelInWay(tile, z_min, false)) {
 					_terraform_err_tile = tile; // highlight the tile above the tunnel
 					return_cmd_error(STR_ERROR_EXCAVATION_WOULD_DAMAGE);
 				}