LookupGrid: fix error when select does not return any result

Controls.LookupGrid/frmLookupGrid.vb

@@ -96,8 +96,10 @@ Public Class frmLookupGrid
         _View.BestFitColumns()
 
         ' Datenspalte zusätzlich in der Breite anpassen
-        Dim oDataColumn As GridColumn = _View.Columns.Item(_DataColumn)
-        oDataColumn.BestFit()
+        If _View.Columns.Count = 0 Then
+            Dim oDataColumn As GridColumn = _View.Columns.Item(_DataColumn)
+            oDataColumn.BestFit()
+        End If
     End Sub
     Private Sub frmLookupGrid_Shown(sender As Object, e As EventArgs) Handles Me.Shown
         BringToFront()