In Mu::parse_date_time, when provided with an empty string, return
time_t_max instead of G_MAXINT64. For systems with a 64-bit time_t, there
is no difference. With a 32-bit time_t it caused a test to fail:
not ok /utils/date-basic - ERROR:../mu-1.12.4/lib/utils/tests/test-utils.cc:92
void test_date_basic(): assertion failed
(parse_date_time(std::get<0>(test), std::get<1>(test)).value_or(-1)
== std::get<2>(test)): (18446744073709551615 == 2147483647)
This edge case probably only affected the test, as when other parts of
the application call parse_date_time (e.g. mu-server.cc and
mu-query-processor.cc), they check if the input string is empty first.
075394b35f