When implementing proper ownership `acquire()` and `release()` semantics
for `NativeWindow` in #207, I
thought I had checked all existing calls to `NativeWindow::from_ptr()`
to make sure that they return a pointer that we get ownership over, and
have to clean up ourselves.  This turns out to [not be the case for
`AImageReader_getWindow()`]:

    The ANativeWindow is managed by this image reader. Do NOT call ANativeWindow_release on it. Instead, use AImageReader_delete.

And can be trivially reproduced by creating an `ImageReader` and calling
`.get_window()`.  Dropping the `NativeWindow` is fine but subsequently
dropping the `ImageReader` results in a NULL-pointer SEGFAULT.

For now calling `clone_from_ptr()` is enough to first acquire an extra
reference on the pointer so that ownership remains balanced, but in the
future we'd like to investigate a [new non-owned `NativeWindow` type
similar to `HardwareBuffer`].

As of writing the following calls to `from_ptr()` remain, that are all
confirmed to transfer ownership and require cleanup via `_release()`:
- `ASurfaceTexture_acquireANativeWindow()`;
- `AMediaCodec_createInputSurface()`;
- `AMediaCodec_createPersistentInputSurface()`;
- `ANativeWindow_fromSurface()`.

[not be the case for `AImageReader_getWindow()`]: https://developer.android.com/ndk/reference/group/media#aimagereader_getwindow
[new non-owned `NativeWindow` type similar to `HardwareBuffer`]: #309