Fix and test fallible return of Vec from C to Rust
diff --git a/tests/ffi/lib.rs b/tests/ffi/lib.rs
index 0965e52..6e636d8 100644
--- a/tests/ffi/lib.rs
+++ b/tests/ffi/lib.rs
@@ -61,6 +61,7 @@
         fn c_try_return_sliceu8(s: &[u8]) -> Result<&[u8]>;
         fn c_try_return_rust_string() -> Result<String>;
         fn c_try_return_unique_ptr_string() -> Result<UniquePtr<CxxString>>;
+        fn c_try_return_rust_vec() -> Result<Vec<u8>>;
 
         fn get(self: &C) -> usize;
         fn set(self: &mut C, n: usize) -> usize;