[PATCH] ntdll: Fix converting large 32-bit time_t when time_t is signed.

[Erich E. Hoover]

Found this while trying to fix something else.  If time_t is treated
as signed (32-bit Linux) and you have a time_t value where the high
bit is set then when you convert it to 64-bit you get an improperly
sign-extended value.  See the included test for an example (make sure
you run the 32-bit tests).

Best,
Erich