Minor improvments to NSE code
Summary:
This differential addresses two issues that Ashoat discovered in my past diffs. The first one: https://phab.comm.dev/D7814, the second one:
https://phab.comm.dev/D8795.
Test Plan: Build iOS app and ensure encrypted notifications are working as previously.
Reviewers: tomek, ashoat
Reviewed By: ashoat
Subscribers: wyilio
Differential Revision: https://phab.comm.dev/D9400