Prevent crash when adding group member by username.

app/src/main/java/org/thoughtcrime/securesms/ContactSelectionListFragment.java

@@ -667,7 +667,7 @@ public final class ContactSelectionListFragment extends LoggingFragment
       SelectedContact selectedContact = contact.isUsernameType() ? SelectedContact.forUsername(contact.getRecipientId().orElse(null), contact.getNumber())
                                                                  : SelectedContact.forPhone(contact.getRecipientId().orElse(null), contact.getNumber());
 
-      if (!canSelectSelf && Recipient.self().getId().equals(selectedContact.getOrCreateRecipientId(requireContext()))) {
+      if (!canSelectSelf && !selectedContact.hasUsername() && Recipient.self().getId().equals(selectedContact.getOrCreateRecipientId(requireContext()))) {
         Toast.makeText(requireContext(), R.string.ContactSelectionListFragment_you_do_not_need_to_add_yourself_to_the_group, Toast.LENGTH_SHORT).show();
         return;
       }

app/src/main/java/org/thoughtcrime/securesms/contacts/SelectedContact.java

@@ -46,6 +46,10 @@ public final class SelectedContact {
     }
   }
 
+  public boolean hasUsername() {
+    return username != null;
+  }
+
   /**
    * Returns true when non-null recipient ids match, and false if not.
    * <p>