Revert "Restore threads in single column mode too"

This reverts commit 6f2913430f.

app/src/main/java/eu/faircode/email/ActivityView.java

@@ -725,7 +725,7 @@ public class ActivityView extends ActivityBilling implements FragmentManager.OnB
             drawerToggle.setDrawerIndicatorEnabled(savedInstanceState.getBoolean("fair:toggle"));
 
             Intent thread = savedInstanceState.getParcelable("fair:thread");
-            if (thread != null) {
+            if (thread != null && content_pane != null) {
                 getSupportFragmentManager().popBackStack("thread", FragmentManager.POP_BACK_STACK_INCLUSIVE);
                 onViewThread(thread);
             }
@@ -1342,18 +1342,18 @@ public class ActivityView extends ActivityBilling implements FragmentManager.OnB
                 drawerLayout.closeDrawer(drawerContainer);
             drawerToggle.setDrawerIndicatorEnabled(count == 1);
 
-            boolean thread = "thread".equals(getSupportFragmentManager().getBackStackEntryAt(count - 1).getName());
-            if (!thread)
-                lastThread = null;
-
             if (content_pane != null) {
                 SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);
                 boolean close_pane = prefs.getBoolean("close_pane", !Helper.isSurfaceDuo());
+                boolean thread = "thread".equals(getSupportFragmentManager().getBackStackEntryAt(count - 1).getName());
                 Fragment fragment = getSupportFragmentManager().findFragmentById(R.id.content_pane);
 
                 int visibility = (!thread || fragment == null ? (close_pane ? View.GONE : View.INVISIBLE) : View.VISIBLE);
                 content_separator.setVisibility(visibility);
                 content_pane.setVisibility(visibility);
+
+                if (!thread)
+                    lastThread = null;
             }
         }
     }