ae.c: set errno when error is not a failing syscall.
ae.c: set errno when error is not a failing syscall.

In this way the caller is able to perform better error checking or to
use strerror() without the risk of meaningless error messages being
displayed.

JackieXie168/redis,JackieXie168/redis,JackieXie168/redis,JackieXie168/redis