Also, handle the case where 'read' returns EINVAL instead of EBADF
when the descriptor is not ready. (android 4.4.4/cyanogenmod, nexus7)

Change-Id: I56c5949d27303d44a4fd0de38951b85e20cef167
Reviewed-on: https://go-review.googlesource.com/15810Reviewed-by: Ian Lance Taylor <iant@golang.org>