Fixed global variable buffer read overflow [#CLICKHOUSE-4191]

dbms/tests/queries/0_stateless/00801_daylight_saving_time_hour_underflow.reference

+0	xxxx-xx-xx xx:xx:xx	1	xxxx-xx-xx xx:xx:xx; xx:xx:xx; xxxx-xx-xx xx:xx:xx

dbms/tests/queries/0_stateless/00801_daylight_saving_time_hour_underflow.sql

+-- See comment in DateLUTImpl.cpp: "We doesn't support cases when time change results in switching to previous day..."
+SELECT
+    ignore(toDateTime(370641600, 'Europe/Moscow') AS t),
+    replaceRegexpAll(toString(t), '\\d', 'x'),
+    toHour(t) < 24,
+    replaceRegexpAll(formatDateTime(t, '%Y-%m-%d %H:%M:%S; %R:%S; %F %T'), '\\d', 'x');