gen1/2 shiny button fix

setting the string to the control causes it to update, use the
changingFields to prevent this update from happening until we want to
(via UpdateIVs)
Closes #1444

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

@@ -1593,10 +1593,12 @@ private void UpdateShiny(bool PID)
             else
             {
                 pkm.SetShinyIVs();
+                changingFields = true;
                 TB_ATKIV.Text = pkm.IV_ATK.ToString();
                 TB_DEFIV.Text = pkm.IV_DEF.ToString();
                 TB_SPEIV.Text = pkm.IV_SPE.ToString();
                 TB_SPAIV.Text = pkm.IV_SPA.ToString();
+                changingFields = true;
                 UpdateIVs(null, null);
             }