test: fix epoll_wait() usage in test-embed.c
test: fix epoll_wait() usage in test-embed.c

Passing 0 as the `maxevents` argument fails with EINVAL, passing NULL as
the `events` argument fails with EFAULT.

Fixes #915.

unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso