DeliveryAdminWindow: Invalidate non-positive weight

Elwig/ViewModels/DeliveryAdminViewModel.cs

@@ -117,7 +117,7 @@ namespace Elwig.ViewModels {
         public partial string? WeightString { get; set; }
         public int? Weight {
             get => int.TryParse(WeightString?.Replace(Utils.GroupSeparator, ""), out var w) ? w : null;
-            set => WeightString = $"{value:N0}";
+            set => WeightString = value > 0 ? $"{value:N0}" : null;
         }
         [ObservableProperty]
         public partial string? TareString { get; set; } = "-";

Elwig/Windows/DeliveryAdminWindow.xaml.cs

@@ -629,7 +629,7 @@ namespace Elwig.Windows {
             var correction = Utils.ShowTareCorrectionDialog(ViewModel.ActualTare, ViewModel.TargetTare);
             if (correction == null) return;
             ViewModel.Weight += lastCorrection - correction;
-            if (ViewModel.WeighingData is string s) {
+            if (ViewModel.Weight != null && ViewModel.WeighingData is string s) {
                 ViewModel.TargetTare = correction == 0 ? null : (ViewModel.ActualTare ?? 0) + correction;
                 ViewModel.Tare = ViewModel.TargetTare ?? ViewModel.ActualTare;
                 var obj = JsonNode.Parse(s)!.AsObject();
@@ -1514,7 +1514,7 @@ namespace Elwig.Windows {
         }
 
         private void WeightInput_TextChanged(object sender, TextChangedEventArgs evt) {
-            InputTextChanged((TextBox)sender);
+            InputTextChanged((TextBox)sender, new ValidationResult(ViewModel.Weight > 0, null));
         }
 
         private void TemperatureAcidInput_TextChanged(object sender, TextChangedEventArgs evt) {