Add save/load support for train speed adaptation

src/saveload/extended_ver_sl.cpp

@@ -151,6 +151,7 @@ const SlxiSubChunkInfo _sl_xv_sub_chunk_infos[] = {
 	{ XSLFI_WATER_FLOODING,         XSCF_NULL,                2,   2, "water_flooding",            nullptr, nullptr, nullptr        },
 	{ XSLFI_MORE_HOUSES,            XSCF_NULL,                2,   2, "more_houses",               nullptr, nullptr, nullptr        },
 	{ XSLFI_CUSTOM_TOWN_ZONE,       XSCF_IGNORABLE_UNKNOWN,   1,   1, "custom_town_zone",          nullptr, nullptr, nullptr        },
+	{ XSLFI_TRAIN_SPEED_ADAPTATION, XSCF_NULL,                1,   1, "train_speed_adaptation",    nullptr, nullptr, "TSAS"         },
 	{ XSLFI_NULL, XSCF_NULL, 0, 0, nullptr, nullptr, nullptr, nullptr },// This is the end marker
 };