title: Crash in SessionDelegate.swift line 93
body: <p>I am experiencing a crash when invoking cancelDownloadTask()
  Do you have any idea whether the crash might be caused by Kingfisher?</p>
  
  <p><a href="https://pastebin.com/r9J0Bepe" rel="nofollow noreferrer">Crashlog</a></p>
  
  <p>I'm using Kingfisher 5.0.1 and I'm calling function from Deprecated.swift</p>
  
  <pre><code>public func setImage(with resource: Resource?,
                           placeholder: Placeholder? = nil,
                           options: KingfisherOptionsInfo? = nil,
                           progressBlock: DownloadProgressBlock? = nil,
                           completionHandler: CompletionHandler?) -&gt; DownloadTask?
  </code></pre>
  
  <p>Unfortunately the reproduction is quite low and I am loading many small images.</p>
  
  <p>Have you ever encountered such issue with the library? HttpParser is very strange at the beginning of the crashlog. Do you have any idea what might be the cause of it. </p>
  
  <p>Regards
  Greg</p>