Do not use a boards submenu with just one platform

When just one platform is installed, it does not make much sense to use
a submenu, so just add the boards directly under the boards menu as
before.

app/src/processing/app/Base.java

@@ -1468,18 +1468,30 @@ public void actionPerformed(ActionEvent actionevent) {
     ButtonGroup boardsButtonGroup = new ButtonGroup();
     Map<String, ButtonGroup> buttonGroupsMap = new HashMap<>();
 
+    int platformCount = 0;
+    for (TargetPackage targetPackage : BaseNoGui.packages.values()) {
+      for (TargetPlatform targetPlatform : targetPackage.platforms()) {
+        ++platformCount;
+      }
+    }
+
     // Cycle through all packages
     for (TargetPackage targetPackage : BaseNoGui.packages.values()) {
       // For every package cycle through all platform
       for (TargetPlatform targetPlatform : targetPackage.platforms()) {
+        JMenu platformBoardsMenu;
+        if (platformCount == 1) {
+          // With just single platform, just add all platforms directly
+          platformBoardsMenu = boardMenu;
+        } else {
+          // Add a submenu for each platform
+          String platformLabel = targetPlatform.getPreferences().get("name");
+          if (platformLabel == null)
+            platformLabel = targetPackage.getId() + "-" + targetPlatform.getId();
 
-        // Add a title for each platform
-        String platformLabel = targetPlatform.getPreferences().get("name");
-        if (platformLabel == null)
-          platformLabel = targetPackage.getId() + "-" + targetPlatform.getId();
-
-        JMenu platformBoardsMenu = new JMenu(tr(platformLabel));
-        boardMenu.add(platformBoardsMenu);
+          platformBoardsMenu = new JMenu(tr(platformLabel));
+          boardMenu.add(platformBoardsMenu);
+        }
 
         // Cycle through all boards of this platform
         for (TargetBoard board : targetPlatform.getBoards().values()) {