Skip writing PFD status when comm is closed.

If the remote side of PFD has already written a status message, then
they've also closed their end of the comm FD, and we're going to
EPIPE if we try sending our own status.  So, skip writing status if
a remote status is present.

Only one end of the openFile() comm socket needs to be blocking,
otherwise detachFd() would end up blocking forever.

Bug: 11385467
Change-Id: I346d40cc1ca4a6683cec4c2d2b7db2b32ac94a55