Key Selection dialog: double-click on the table header throws unhandled exception

[i3v]

Sometimes, when user double-clicks on the table header e.g. on the "Source", in the "Select a Key" dialog (aka "Show selection dialog when a client program requests a list of keys"), an unhandled exception is generated:

************** Exception Text **************
System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index
   at System.Collections.ArrayList.get_Item(Int32 index)
   at System.Windows.Forms.DataGridViewRowCollection.SharedRow(Int32 rowIndex)
   at System.Windows.Forms.DataGridViewRowCollection.get_Item(Int32 index)
   at dlech.SshAgentLib.WinForms.KeyPicker.keyDataGridView_CellDoubleClick(Object sender, DataGridViewCellEventArgs e)
   at System.Windows.Forms.DataGridView.OnCellDoubleClick(DataGridViewCellEventArgs e)
   at System.Windows.Forms.DataGridView.OnDoubleClick(EventArgs e)
   at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

The following issues could be related: #313, #354.