Fix potential crash & apply code convention

SessionMessagingKit/Messages/Control Messages/ClosedGroupControlMessage.swift

@@ -112,7 +112,7 @@ public final class ClosedGroupControlMessage : ControlMessage {
                 let encryptionKeyPair = coder.decodeObject(forKey: "encryptionKeyPair") as? ECKeyPair,
                 let members = coder.decodeObject(forKey: "members") as? [Data],
                 let admins = coder.decodeObject(forKey: "admins") as? [Data] else { return nil }
-                let expireTimer = coder.decodeObject(forKey: "expireTimer") as! UInt32
+                let expireTimer = coder.decodeObject(forKey: "expireTimer") as? UInt32 ?? 0
             self.kind = .new(publicKey: publicKey, name: name, encryptionKeyPair: encryptionKeyPair, members: members, admins: admins, expireTimer: expireTimer)
         case "encryptionKeyPair":
             let publicKey = coder.decodeObject(forKey: "publicKey") as? Data
@@ -179,7 +179,7 @@ public final class ClosedGroupControlMessage : ControlMessage {
                 let expireTimer = closedGroupControlMessageProto.expireTimer
                 let encryptionKeyPair = try ECKeyPair(publicKeyData: encryptionKeyPairAsProto.publicKey.removing05PrefixIfNeeded(), privateKeyData: encryptionKeyPairAsProto.privateKey)
                 kind = .new(publicKey: publicKey, name: name, encryptionKeyPair: encryptionKeyPair,
-                            members: closedGroupControlMessageProto.members, admins: closedGroupControlMessageProto.admins, expireTimer: expireTimer)
+                    members: closedGroupControlMessageProto.members, admins: closedGroupControlMessageProto.admins, expireTimer: expireTimer)
             } catch {
                 SNLog("Couldn't parse key pair.")
                 return nil

SessionMessagingKit/Sending & Receiving/MessageReceiver+Handling.swift

@@ -397,12 +397,10 @@ extension MessageReceiver {
             let infoMessage = TSInfoMessage(timestamp: messageSentTimestamp, in: thread, messageType: .groupCreated)
             infoMessage.save(with: transaction)
         }
-        var configuration: OWSDisappearingMessagesConfiguration
-        if (expireTimer > 0) {
-            configuration = OWSDisappearingMessagesConfiguration(threadId: thread.uniqueId!, enabled: true, durationSeconds: expireTimer)
-        } else {
-            configuration = OWSDisappearingMessagesConfiguration(threadId: thread.uniqueId!, enabled: false, durationSeconds: 24 * 60 * 60)
-        }
+        let isExpirationTimerEnabled = (expireTimer > 0)
+        let expirationTimerDuration = (isExpirationTimerEnabled ? expireTimer : 24 * 60 * 60)
+        let configuration = OWSDisappearingMessagesConfiguration(threadId: thread.uniqueId!, enabled: isExpirationTimerEnabled,
+            durationSeconds: expirationTimerDuration)
         configuration.save(with: transaction)
         // Add the group to the user's set of public keys to poll for
         Storage.shared.addClosedGroupPublicKey(groupPublicKey, using: transaction)

SessionMessagingKit/Sending & Receiving/MessageSender+ClosedGroups.swift

@@ -163,7 +163,6 @@ extension MessageSender {
         let members = [String](Set(group.groupMemberIds).union(newMembers))
         let membersAsData = members.map { Data(hex: $0) }
         let adminsAsData = group.groupAdminIds.map { Data(hex: $0) }
-        // Get expiration timer value for the group
         let expireTimer = thread.disappearingMessagesDuration(with: transaction)
         guard let encryptionKeyPair = Storage.shared.getLatestClosedGroupEncryptionKeyPair(for: groupPublicKey) else {
             SNLog("Couldn't find encryption key pair for closed group: \(groupPublicKey).")