Common: Show error message when attributes could not be loaded

GUIs.Common/ObjectPropertyDialog/frmObjectPropertyDialog.vb

@@ -170,6 +170,10 @@ Public Class frmObjectPropertyDialog
 
             Dim oAttributes = Await GetAttributesForBusinessEntity(oEntityId)
 
+            If oAttributes.Count = 0 Then
+                MsgBox($"Es konnten keine Attribute für das Objekt '{_ObjectId}' geladen werden!", MsgBoxStyle.Critical, Text)
+            End If
+
             For Each oAttribute As Attribute In oAttributes
                 Dim oControl = _Controls.GetControlForAttribute(oAttribute, True)
                 Dim oItem As LayoutControlItem = AttributeLayout.AddItem()
@@ -230,4 +234,8 @@ Public Class frmObjectPropertyDialog
             Return False
         End Try
     End Function
+
+    Private Sub TabFormControl1_Click(sender As Object, e As EventArgs) Handles TabFormControl1.Click
+
+    End Sub
 End Class