compability with curl before 7.20.0
compability with curl before 7.20.0

curl before 7.20.0 can return CURLM_CALL_MULTI_PERFORM, when that happens
continue so we call it immeadiately again.

Yubico/yubico-c-client,kellyjf/yubi,Yubico/yubico-c-client,kellyjf/yubi,Yubico/yubico-c-client