minor refactor

SessionMessagingKit/Open Groups/OpenGroupManagerV2.swift

@@ -34,7 +34,7 @@ public final class OpenGroupManagerV2 : NSObject {
         let transaction = transaction as! YapDatabaseReadWriteTransaction
         let groupId: Data = LKGroupUtilities.getEncodedOpenGroupIDAsData("\(server).\(room)")
         
-        if OpenGroupManagerV2.shared.pollers[server] != nil && TSGroupThread.fetch(uniqueId: TSGroupThread.threadId(fromGroupId: groupId), transaction: transaction) != nil {
+        if OpenGroupManagerV2.shared.pollers[server] != nil && TSGroupThread.fetch(groupId: groupId, transaction: transaction) != nil {
             SNLog("Ignoring join open group attempt (already joined)")
             return Promise.value(())
         }

SessionMessagingKit/Threads/TSGroupThread.h

@@ -30,7 +30,8 @@ extern NSString *const TSGroupThread_NotificationKey_UniqueId;
                                    groupType:(GroupType) groupType
                                  transaction:(YapDatabaseReadWriteTransaction *)transaction;
 
-+ (nullable instancetype)threadWithGroupId:(NSData *)groupId transaction:(YapDatabaseReadTransaction *)transaction;
++ (nullable instancetype)threadWithGroupId:(NSData *)groupId transaction:(YapDatabaseReadTransaction *)transaction
+    NS_SWIFT_NAME(fetch(groupId:transaction:));
 
 + (NSString *)threadIdFromGroupId:(NSData *)groupId;