Fixes:

```rust
error: the type `android_injected_glue::ffi::android_app` does not permit zero-initialization
   --> ports/libsimpleservo/jniapi/src/lib.rs:511:46
    |
511 |     let mut app: ffi::android_app = unsafe { std::mem::zeroed() };
    |                                              ^^^^^^^^^^^^^^^^^^
    |                                              |
    |                                              this code causes undefined behavior when executed
    |                                              help: use `MaybeUninit<T>` instead
    |
    = note: `-D invalid-value` implied by `-D warnings`
note: Function pointers must be non-null (in this struct field)
   --> /root/.cargo/registry/src/github.com-1ecc6299db9ec823/android_injected_glue-0.2.3/src/ffi.rs:23:5
    |
23  |     pub onAppCmd: extern fn(*mut android_app, i32),
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: aborting due to previous error
```