ZUGFeRDTest: update gui

GUIs.Test.ZUGFeRDTest/Form1.vb

@@ -105,10 +105,13 @@ Public Class Form1
         Dim oArgs As New WorkerArgs()
 
         If oResult = DialogResult.OK Then
-            Dim oDoc = _zugferd.ValidateZUGFeRDFileWithGDPicture(OpenFileDialog1.FileName)
-            Dim oZUGFERD = _zugferd.SerializeZUGFeRDDocument(oDoc)
-            Console.WriteLine()
-
+            Try
+                Dim oDoc = _zugferd.ValidateZUGFeRDFileWithGDPicture(OpenFileDialog1.FileName)
+                Dim oZUGFERD = _zugferd.SerializeZUGFeRDDocument(oDoc)
+                Console.WriteLine()
+            Catch ex As Exception
+                MsgBox(ex.Message)
+            End Try
         End If
     End Sub