fix(ui): tapping the same right-pane item twice in landscape opened it twice

openPane()/openPaneFragment() always pushed a new back-stack entry on
the right pane's child FragmentManager, even when the fragment being
opened was already the one on screen. A quick double-tap on the same
trigger (instance row, settings gear, etc.) therefore stacked two
identical entries, and Back had to be pressed twice to actually get
back to the pane's home screen — the first press just popped the
duplicate back to itself.

Added isTagAlreadyOnTop(), checked at the top of both navigation
helpers: if the requested tag is already the top back-stack entry,
the tap is a no-op instead of pushing a duplicate.

Author: MaxJubayerYT

app_pojavlauncher/src/main/assets/amethyst.png

@@ -157,9 +157,24 @@ private void openModStore() {
         openPaneFragment(fragment, ModsSearchFragment.TAG);
     }
 
+    /**
+     * True if {@code tag} is already the top entry on the right pane's back stack —
+     * i.e. that fragment is already showing. Used to swallow a double-tap on the
+     * same trigger instead of pushing a second, identical back-stack entry (which
+     * made Back have to be pressed twice to actually leave).
+     */
+    private boolean isTagAlreadyOnTop(String tag) {
+        if (!isTwoPane()) return false;
+        androidx.fragment.app.FragmentManager fm = getChildFragmentManager();
+        int count = fm.getBackStackEntryCount();
+        if (count == 0) return false;
+        return tag.equals(fm.getBackStackEntryAt(count - 1).getName());
+    }
+
     /** Navigate to a pre-built fragment instance (preserves args on fresh instances). */
     private void openPaneFragment(Fragment fragment, String tag) {
         if (isTwoPane()) {
+            if (isTagAlreadyOnTop(tag)) return; // already showing — ignore the double-tap
             getChildFragmentManager()
                     .beginTransaction()
                     .setReorderingAllowed(true)
@@ -179,6 +194,7 @@ private void openPaneFragment(Fragment fragment, String tag) {
     private void openPane(Class<? extends Fragment> fragmentClass, String tag,
                           @Nullable Bundle args) {
         if (isTwoPane()) {
+            if (isTagAlreadyOnTop(tag)) return; // already showing — ignore the double-tap
             getChildFragmentManager()
                     .beginTransaction()
                     .setReorderingAllowed(true)