Don't try to truncate zooms if we are still tiling at z18

tile.cpp

@@ -1589,7 +1589,7 @@ long long write_tile(decompressor *geoms, std::atomic<long long> *geompos_in, ch
 		// empirical estimate from ne_10m_admin_0_countries, CPAD units, Cal fires.
 		// only try to make an overzoomable final tile if it seems like it might work
 		long long estimated_output_tile_size = 0.6693 * estimated_complexity - 3.36e+04;
-		if (estimated_output_tile_size < (long long) (0.9 * max_tile_size)) {
+		if (estimated_output_tile_size < (long long) (0.9 * max_tile_size) && 30 - z > detail) {
 			first_detail = 30 - z;
 			second_detail = detail;
 			trying_to_stop_early = true;