BannedContactModel: check if entry exists

Sometimes contact method could be added to BannedContactModel twice:
during creating model and from accountModel when receiving
slotContactRemoved.(it happens if account does not have bannedContactModel
yet). This patch fix it by checking if ContactMethod already exists in the
banned contact list.

Change-Id: I514e0301bbc07378ef9f9a5c345db5b49c8e23e0
Reviewed-by: Anthony Léonard <anthony.leonard@savoirfairelinux.com>

src/bannedcontactmodel.cpp

@@ -137,6 +137,8 @@ BannedContactModel::columnCount( const QModelIndex& parent ) const
 void
 BannedContactModel::add(ContactMethod* cm)
 {
+    if (d_ptr->m_lBanned.contains(cm))
+        return;
     beginInsertRows(QModelIndex(),d_ptr->m_lBanned.size(),d_ptr->m_lBanned.size());
     d_ptr->m_lBanned << cm;
     endInsertRows();