gstreamer/allocation_params: Implement to_glib_none

This is needed by the now-autogenerated implementation of
Allocator::alloc, and later on the GL bindings.

gstreamer/src/allocation_params.rs

@@ -56,3 +56,12 @@ impl From<ffi::GstAllocationParams> for AllocationParams {
         AllocationParams(params)
     }
 }
+
+#[doc(hidden)]
+impl<'a> ToGlibPtr<'a, *const ffi::GstAllocationParams> for AllocationParams {
+    type Storage = &'a Self;
+
+    fn to_glib_none(&'a self) -> Stash<'a, *const ffi::GstAllocationParams, Self> {
+        Stash(&self.0, self)
+    }
+}