When the application just started the transfer and then stops it while
the name resolve in the background thread hasn't completed, we need to
wait for the resolve to complete and then cleanup data accordingly.
Enabled test 1553 again and added test 1590 to also check when the host
name resolves successfully.
Detected by OSS-fuzz.
Closes#1968
When imap_done() got called before a connection is setup, it would try
to "finish up" and dereffed a NULL pointer.
Test case 1553 managed to reproduce. I had to actually use a host name
to try to resolve to slow it down, as using the normal local server IP
will make libcurl get a connection in the first curl_multi_perform()
loop and then the bug doesn't trigger.
Fixes#1953
Assisted-by: Max Dymond
