initial_snapshot: Accept unknown "emojiset" values

lib/api/model/initial_snapshot.dart

@@ -295,6 +295,7 @@ class UserSettings {
   TwentyFourHourTimeMode twentyFourHourTime;
 
   bool displayEmojiReactionUsers;
+  @JsonKey(unknownEnumValue: Emojiset.unknown)
   Emojiset emojiset;
   bool presenceEnabled;
 

lib/api/model/model.dart

@@ -390,7 +390,8 @@ enum Emojiset {
   google,
   googleBlob,
   twitter,
-  text;
+  text,
+  unknown;
 
   /// Get an [Emojiset] from a raw string. Throws if the string is unrecognized.
   ///

test/api/model/initial_snapshot_test.dart

@@ -62,4 +62,19 @@ void main() {
       'unread_message_ids': [11, 2, 3],
     })).throws<AssertionError>();
   });
+
+  test('UserSettings.emojiset handles various unknown values', () {
+    final unknownValues = ['apple', 'microsoft', 'facebook', ''];
+    for (final unknownValue in unknownValues) {
+      final settings = UserSettings.fromJson({
+        'twenty_four_hour_time': true,
+        'display_emoji_reaction_users': true,
+        'emojiset': unknownValue,
+        'presence_enabled': true,
+      });
+
+      // Verify unknown emojiset defaults to Emojiset.unknow
+      check(settings.emojiset).equals(Emojiset.unknown);
+    }
+  });
 }