[bindings] Fix CVecTempl clone operation behavior.

CVecTempl previously called Vec.clone_from_slice() on a
newly-allocated Vec, which immediately panics as
[T].clone_from_slice() requires that the Vec/target slice already
has the same length as the source slice. This should have been
Vec.extend_from_slice() which exhibits the correct behavior.

Author: TheBlueMatt

lightning-c-bindings/src/c_types/mod.rs

@@ -320,7 +320,7 @@ impl<T: Clone> Clone for CVecTempl<T> {
 	fn clone(&self) -> Self {
 		let mut res = Vec::new();
 		if self.datalen == 0 { return Self::from(res); }
-		res.clone_from_slice(unsafe { std::slice::from_raw_parts_mut(self.data, self.datalen) });
+		res.extend_from_slice(unsafe { std::slice::from_raw_parts_mut(self.data, self.datalen) });
 		Self::from(res)
 	}
 }