Fix crash when there are duplicate emojis

Closes #164

Tusker/Screens/Compose/ComposeAutocompleteView.swift

@@ -256,13 +256,19 @@ struct ComposeAutocompleteEmojisView: View {
         }
         
         mastodonController.getCustomEmojis { (emojis) in
-            self.emojis =
+            let emojis: [Emoji] =
                 emojis.map { (emoji) -> (Emoji, (matched: Bool, score: Int)) in
                     (emoji, FuzzyMatcher.match(pattern: query, str: emoji.shortcode))
                 }
                 .filter(\.1.matched)
                 .sorted { $0.1.score > $1.1.score }
                 .map(\.0)
+            var shortcodes = Set<String>()
+            self.emojis = []
+            for emoji in emojis where !shortcodes.contains(emoji.shortcode) {
+                self.emojis.append(emoji)
+                shortcodes.insert(emoji.shortcode)
+            }
         }
     }
 }