refactor: don't delete empty threads if they're open groups

app/src/main/java/org/thoughtcrime/securesms/database/ThreadDatabase.java

@@ -513,9 +513,9 @@ public class ThreadDatabase extends Database {
     MmsSmsDatabase mmsSmsDatabase = DatabaseFactory.getMmsSmsDatabase(context);
     long count                    = mmsSmsDatabase.getConversationCount(threadId);
 
+    boolean shouldDeleteEmptyThread = deleteThreadOnEmpty(threadId);
 
-
-    if (count == 0) {
+    if (count == 0 && shouldDeleteEmptyThread) {
       deleteThread(threadId);
       notifyConversationListListeners();
       return true;
@@ -534,9 +534,12 @@ public class ThreadDatabase extends Database {
         notifyConversationListListeners();
         return false;
       } else {
-        deleteThread(threadId);
-        notifyConversationListListeners();
-        return true;
+        if (shouldDeleteEmptyThread) {
+          deleteThread(threadId);
+          notifyConversationListListeners();
+          return true;
+        }
+        return false;
       }
     } finally {
       if (reader != null)
@@ -544,6 +547,11 @@ public class ThreadDatabase extends Database {
     }
   }
 
+  private boolean deleteThreadOnEmpty(long threadId) {
+    Recipient threadRecipient = getRecipientForThreadId(threadId);
+    return threadRecipient != null && !threadRecipient.isOpenGroupRecipient();
+  }
+
   private @NonNull String getFormattedBodyFor(@NonNull MessageRecord messageRecord) {
     if (messageRecord.isMms()) {
       MmsMessageRecord record = (MmsMessageRecord) messageRecord;

app/src/main/java/org/thoughtcrime/securesms/groups/GroupManager.java

@@ -70,10 +70,6 @@ public class GroupManager {
     final ThreadDatabase threadDatabase = DatabaseFactory.getThreadDatabase(context);
     final Recipient      groupRecipient = Recipient.from(context, Address.fromSerialized(groupId), false);
 
-    if (!groupDatabase.getGroup(groupId).isPresent()) {
-      return false;
-    }
-
     long threadId = threadDatabase.getThreadIdIfExistsFor(groupRecipient);
     if (threadId != -1L) {
       threadDatabase.deleteConversation(threadId);