Fix Sentinel Leak on Sibling Exports Too

[slick-daddy]

Emulator Version / Commit

v0.0.4

Bug Description

The same sentinel leak exists in the sibling POSIX exports in
KernelFileExtendedExports.cs (pread, pwrite, ftruncate, truncate,
fsync, rename, dup, dup2, fcntl). They aren't on this crash path,
so they're intentionally left for a separate PR using the same
PosixFailure wrapper.

Origanally posted on #461 as Follow up

Log File