better handling of invalid zugferd files

Jobs/Exceptions.vb

@@ -21,6 +21,14 @@ Public Class Exceptions
         End Sub
     End Class
 
+    Public Class InvalidFerdException
+        Inherits ApplicationException
+
+        Public Sub New()
+            MyBase.New("ZUGFeRD document found but was not formatted correctly")
+        End Sub
+    End Class
+
     Public Class NoFerdsException
         Inherits ApplicationException