Make FILE*s less usable after fclose(3).

Make FILE*s less usable after fclose(3).

BSD doesn't invalidate the fd stored in struct FILE, which can make
it possible (via fileno(3), for example), to perform operations on
an fd you didn't intend to (rather than just failing with EBADF).

Fixing this makes the code slightly simpler anyway, and might help
catch bad code before it ships.

Bug: http://stackoverflow.com/questions/10816837/fclose-works-differently-on-android-and-linux
Change-Id: I9db74584038229499197a2695c70b58ed0372a87