Notify event pipe before releasing NativeActivity resources

The design of ndk-glue seems to imply that the user of a `NativeActivity`
resource, e.g. `NativeWindow` obtained from `ndk_glue::native_window()`, should
hold a read lock on the resource as long as they are using it.

Therefore, ndk-glue's `NativeActivity` callbacks related to resource release
should: (1) notify the user of upcoming resource release (2) acquire a write
lock on the handle, waiting for all read locks to be dropped, (3) drop the
handle, (4) return from the callback.  This allows the user to correctly
release various objects derived from the resource (e.g. `EGLSurface` from
`NativeWindow`) before it goes away.  Currently, the order is 2-3-1-4, which
can lead to a deadlock or a race condition, if the user drops the read lock at
some earlier point while continuing to use objects derived from the resource.

This commit fixes the order.

ndk-glue/src/lib.rs

@@ -260,8 +260,8 @@ unsafe extern "C" fn on_window_destroyed(
     activity: *mut ANativeActivity,
     _window: *mut ANativeWindow,
 ) {
-    *NATIVE_WINDOW.write().unwrap() = None;
     wake(activity, Event::WindowDestroyed);
+    *NATIVE_WINDOW.write().unwrap() = None;
 }
 
 unsafe extern "C" fn on_input_queue_created(
@@ -279,10 +279,12 @@ unsafe extern "C" fn on_input_queue_destroyed(
     activity: *mut ANativeActivity,
     queue: *mut AInputQueue,
 ) {
+    wake(activity, Event::InputQueueDestroyed);
     let input_queue = InputQueue::from_ptr(NonNull::new(queue).unwrap());
+    let mut input_queue_lock = INPUT_QUEUE.write().unwrap();
+    assert!(input_queue_lock.as_ref().unwrap().ptr() == input_queue.ptr());
     input_queue.detach_looper();
-    *INPUT_QUEUE.write().unwrap() = None;
-    wake(activity, Event::InputQueueDestroyed);
+    *input_queue_lock = None;
 }
 
 unsafe extern "C" fn on_content_rect_changed(activity: *mut ANativeActivity, rect: *const ARect) {