ExternsionsMP: fix ShowUserControl minimize bug (#3479)

When minimizing a form generated by ShowUserControl, the client size
gets set to 0, which causes issues when the form is restored. Sizes
should only be copied when the window state is normal.

Utilities/ExtensionsMP.cs

@@ -135,8 +135,8 @@ private static void Ctl_SizeChanged(object sender, EventArgs e)
             var frm = ctl.Tag as Form;
             if (frm == null)
                 return;
-
-            frm.ClientSize = ctl.ClientSize;
+            if (frm.WindowState == FormWindowState.Normal)
+                frm.ClientSize = ctl.ClientSize;
         }
 
         private static void Frm_Closing(object sender, System.ComponentModel.CancelEventArgs e)