[NaCl SDK] nacl_io: Fix select() implementation so it doesn't assume entire fd_sets.

Turns out the application code (specifically openssh does
this) is allows to pass incomplete fd_set structs as long
as they can store at least nfds worth of information.
This means that we can't call FD_ZERO on the pointers
given to use since FD_ZERO assumes a full fd_set.

This fixed a long standing memory corruption issue with
openssh.

R=binji@chromium.org

Review URL: https://codereview.chromium.org/229863002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@262849 0039d316-1c4b-4281-b951-d872f2087c98
2 files changed