The delay is caused because some Commands are only called in certain
interval(called refreshInterval, default, 1000ms). In aria2 download
stops when all Commands associated to it are stopped. Since some
Commands are called in each 1000ms by default, as mentioned before, we
have to wait for them. To fix this issue, we call
DownloadEngine::setRefreshInterval(0) when pausing/stopping downloads.
DownloadEngine::setRefreshInterval(0) makes refreshInterval 0 in one
shot.
When all segments are ignored, now DownloadFailureException is thrown.
And stop the download immediately. As described earlier, we call
DownloadEngine::setRefreshInterval(0) in catch block of
DownloadFailureException to eliminate delay.
