(svn r21732) -Fix (r21728): show the "proper" error that the landscaping limit is reached instead of "already flat"

src/terraform_cmd.cpp

@@ -422,6 +422,7 @@ CommandCost CmdLevelLand(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32
 
 	const Company *c = Company::GetIfValid(_current_company);
 	int limit = (c == NULL ? INT32_MAX : GB(c->terraform_limit, 16, 16));
+	if (limit == 0) return_cmd_error(STR_ERROR_TERRAFORM_LIMIT_REACHED);
 
 	TileArea ta(tile, p1);
 	TileIterator *iter = HasBit(p2, 0) ? (TileIterator *)new DiagonalTileIterator(tile, p1) : new OrthogonalTileIterator(ta);