Check for null in LocalSocketImpl.SocketInputStream.available()

Calling available() on a local socket after close() will cause a native
crash. Other methods that pass LocalSocketImpl.fd to native code copy
the fd and check for null.

https://android-review.googlesource.com/#/c/90900/

Change-Id: I2d0b573f34ae47a23009760bbb1c02933ab0a20e
Signed-off-by: houst0nn <houstonn@gmail.com>
Merge "Check for null in LocalSocketImpl.SocketInputStream.available()" into kitkat