Fixing chopping of Invoice number in Bill Timberline poster to ensure that the error warning comes up.

prs.shared/Posters/Timberline/BillTimberlinePoster.cs

@@ -33,9 +33,16 @@ public class BillTimberlineHeader
     [TypeConverter(typeof(TimberlinePosterStringConverter), 10)]
     public string Vendor { get; set; } = "";
 
+    [Ignore]
+    private string _invoice = "";
+
     [Index(2)]
     [TypeConverter(typeof(TimberlinePosterStringConverter), 15)]
-    public string Invoice { get; set; } = "";
+    public string Invoice
+    {
+        get => _invoice;
+        set => _invoice = TimberlinePosterStringConverter.ConvertString(value, 15);
+    }
 
     [Index(3)]
     [TypeConverter(typeof(TimberlinePosterStringConverter), 30)]