Update pkmeditor GB gui loop behavior

updating HP causes SPD to be updated, which is based on SPA; since SPA
is yet to be updated, we trigger constant updates on an SPA > 15 until
we crash.

just use the SPD IV which is already capped by the pkmdata
(this shouldn't refresh fields anyway when loading... whatever).

Closes #1914

PKHeX.WinForms/Controls/PKM Editor/StatEditor.cs

@@ -103,7 +103,7 @@ private void RefreshDerivedValues(object sender)
             if (pkm.Format < 3)
             {
                 TB_HPIV.Text = pkm.IV_HP.ToString();
-                TB_SPDIV.Text = TB_SPAIV.Text;
+                TB_SPDIV.Text = pkm.IV_SPD.ToString();
 
                 MainEditor.UpdateIVsGB(sender == null);
             }