aio: table lookup: verify ctx pointer
aio: table lookup: verify ctx pointer

Another shortcoming of the table lookup patch was revealed where the pointer
was not being tested before being dereferenced.  Verify this to avoid the
NULL pointer dereference.

Signed-off-by: Benjamin LaHaise <b05c66fa21e46731bb89a779db663748f3df8f6a@kvack.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs