NSE can be blocked until the app resumes and finishes pending decryption

[manuroe]

This is another occurence of #4335 but with a more specific case.

We had a rageshake where NSE was not enable to complete its init. It stayed in the state below. The notification was only "Message"

2021-07-20 00:06:53.190 RiotNSE[332:22459]  [NotificationService] setup: MXBackgroundSyncService init: BEFORE
2021-07-20 00:06:53.191 RiotNSE[332:22459]  [NotificationService] Memory: footprint: 7.80 MB - available: 16.17 MB
2021-07-20 00:06:53.216 RiotNSE[332:22459]  [MXSyncResponseFileStore] readData: File read of 9478 bytes lasted 4ms. Free memory: 15.66 MB
2021-07-20 00:06:53.219 RiotNSE[332:22459]  [MXSyncResponseFileStore] readData: Consersion to model lasted 2ms. Free memory: 15.59 MB
2021-07-20 00:06:53.220 RiotNSE[332:22459]  [MXRealmCryptoStore] setShouldCompactOnLaunch: NO

It was enabled to display any notification until the app resumes:

2021-07-20 00:06:02.363 Riot[254:21541]  [MXRealmCryptoStore] performSessionOperationWithGroupSessionWithId done in 13.872ms
2021-07-20 00:06:02.376 Riot[254:21541]  [MXRealmCryptoStore] performSessionOperationWithGroupSessionWithId done in 12.304ms
2021-07-20 00:33:04.464 Riot[254:19997]  [AppDelegate] applicationWillEnterForeground
2021-07-20 00:33:04.525 Riot[254:21541]  [MXRealmCryptoStore] performSessionOperationWithGroupSessionWithId done in 1622147.971ms
2021-07-20 00:33:04.574 Riot[254:21541]  [MXRealmCryptoStore] performSessionOperationWithGroupSessionWithId done in 48.381ms
2021-07-20 00:33:04.609 Riot[254:21541]  [MXRealmCryptoStore] performSessionOperationWithGroupSessionWithId done in 32.695ms

The log above clearly show that the realm lock was kept by the app.

The app should complete any pending decryption before going to sleep.