multi: always do the COMPLETED procedure/state

It was previously erroneously skipped in some situations.

libtest/libntlmconnect.c wrongly depended on wrong behavior (that it
would get a zero timeout) when no handles are "running" in a multi
handle. That behavior is no longer present with this fix. Now libcurl
will always return a -1 timeout when all handles are completed.

Closes #2733