Prevent focus "stalemates" on Android

* java/org/gnu/emacs/EmacsActivity.java (invalidateFocus1): New
argument resetWhenChildless.
(invalidateFocus): If a toplevel window has no focus window,
transfer focus to the toplevel itself.

java/org/gnu/emacs/EmacsActivity.java

@@ -84,7 +84,7 @@ public class EmacsActivity extends Activity
   };
 
   public static void
-  invalidateFocus1 (EmacsWindow window)
+  invalidateFocus1 (EmacsWindow window, boolean resetWhenChildless)
   {
     if (window.view.isFocused ())
       focusedWindow = window;
@@ -92,7 +92,18 @@ public class EmacsActivity extends Activity
     synchronized (window.children)
       {
 	for (EmacsWindow child : window.children)
-	  invalidateFocus1 (child);
+	  invalidateFocus1 (child, false);
+
+	/* If no focused window was previously detected among WINDOW's
+	   children and RESETWHENCHILDLESS is set (implying it is a
+	   toplevel window), request that it be focused, to avoid
+	   creating a situation where no windows exist focused or can be
+	   transferred the input focus by user action.  */
+	if (focusedWindow == null && resetWhenChildless)
+	  {
+	    window.view.requestFocus ();
+	    focusedWindow = window;
+	  }
       }
   }
 
@@ -110,7 +121,7 @@ public class EmacsActivity extends Activity
     for (EmacsActivity activity : focusedActivities)
       {
 	if (activity.window != null)
-	  invalidateFocus1 (activity.window);
+	  invalidateFocus1 (activity.window, focusedWindow == null);
       }
 
     /* Send focus in- and out- events to the previous and current