Fix playing gifs from a background thread

Tusker/Views/Attachments/AttachmentView.swift

@@ -165,7 +165,9 @@ class AttachmentView: UIImageView, GIFAnimatable {
             if self.attachment.url.pathExtension == "gif" {
                 self.source = .gifData(attachmentURL, data)
                 if self.autoplayGifs {
+                    DispatchQueue.main.async {
                         self.animate(withGIFData: data)
+                    }
                 } else {
                     self.displayImage()
                 }