BannedContactModel: prevent remove() call with invalid args

The application crashes if the ContactMethod given to
BannedContactModel::remove() doesn't exist in the banned list.
Check for existance and no-op if not.

Change-Id: Ifde1c1b9a0c369889c8dabfce20dd8d8937b715b
Reviewed-by: Kateryna Kostiuk <kateryna.kostiuk@savoirfairelinux.com>

src/bannedcontactmodel.cpp

@@ -152,6 +152,8 @@ void
 BannedContactModel::remove(ContactMethod* cm)
 {
     auto rowIndex = d_ptr->m_lBanned.indexOf(cm);
+    if (rowIndex < 0)
+        return;
 
     beginRemoveRows(QModelIndex(), rowIndex, rowIndex);
     d_ptr->m_lBanned.removeAt(rowIndex);