ensure the start button can only be clicked once at a time

src/main/java/forge/gui/home/StartButton.java

@@ -1,9 +1,12 @@
 package forge.gui.home;
 
+import java.awt.event.ActionEvent;
+import java.awt.event.ActionListener;
 import java.awt.event.FocusEvent;
 import java.awt.event.FocusListener;
 
 import javax.swing.JButton;
+import javax.swing.SwingUtilities;
 
 import forge.gui.toolbox.FSkin;
 
@@ -30,5 +33,17 @@ public class StartButton extends JButton {
                 setIcon(FSkin.getIcon(FSkin.ButtonImages.IMG_BTN_START_OVER));
             }
         });
+        
+        addActionListener(new ActionListener() {
+            @Override
+            public void actionPerformed(ActionEvent e) {
+                setEnabled(false);
+                
+                // ensure the click action can resolve before we allow the button to be clicked again
+                SwingUtilities.invokeLater(new Runnable() {
+                    @Override public void run() { setEnabled(true); }
+                });
+            }
+        });
     }
 }