Add Run-Time Check for `struct tm` Conversion Containing Negative Values

The library generates struct tm containing negative values. For example the ISO-formatted time string "2021-09-20T01:28:49.354+02:00" is converted into

struct tm {
  .tm_sec = 49,
  .tm_min = 28,
  .tm_hour = -1,
  .tm_mday = 20
  .tm_mon = 8,
  .tm_year = 121,
  .tm_wday = 1,
  .tm_yday = 262,
  .tm_isdst = 0
}

. The library should check whether the built-in or user-provided time conversion function can cope with such values.