Call slot compression

Doesn't work correctly (data shifted down still persists)

PKHeX.Core/Saves/Substructures/Gen7/PokeListHeader.cs

@@ -79,7 +79,7 @@ namespace PKHeX.Core
             get => PokeListInfo[FOLLOW];
             set
             {
-                if ((ushort)value > 1000)
+                if ((ushort)value > 1000 && value != SLOT_EMPTY)
                     throw new ArgumentException(nameof(value));
                 PokeListInfo[FOLLOW] = (ushort)value;
             }

PKHeX.WinForms/Controls/SAV Editor/SAVEditor.cs

@@ -716,6 +716,9 @@ namespace PKHeX.WinForms.Controls
         public bool ExportSaveFile()
         {
             ValidateChildren();
+            bool reload = SAV is SAV7b b && b.FixPreWrite();
+            if (reload)
+                ReloadSlots();
             return WinFormsUtil.SaveSAVDialog(SAV, SAV.CurrentBox);
         }