touch: don't leak descriptor if fstat(2) fails

If fstat(2) fails the close(2) won't be called, which will leak the
file descriptor.

The idea was borrowed from OpenBSD, where similar patch
was applied for futimens(2).

MFC after: 1 week

(cherry picked from commit cb54c500d0e1a2c52270b15c6db6a88ca3feb86a)