Fix @Published property being changed on background thread

Tusker/API/MastodonController.swift

@@ -321,7 +321,9 @@ class MastodonController: ObservableObject {
             let request = Client.getCustomEmoji()
             run(request) { (response) in
                 if case let .success(emojis, _) = response {
-                    self.customEmojis = emojis
+                    DispatchQueue.main.async {
+                        self.customEmojis = emojis
+                    }
                     completion(emojis)
                 } else {
                     completion([])