[Crypto] Improve Event.getClearContent() and fix assignement issue.

[bmarty]

Type of change

• Feature
• Bugfix
• Technical
• Other :

Content

The first commit should prevent encrypted content to be parsed as decoded Event. Hopefully there will be no side effect. I have checked and this should be fine.
The last commit is fixing an issue, calling RoomService.refreshJoinedRoomSummaryPreviews has never worked as expected with the Crypto Rust SDK.

Motivation and context

Should fix lots of error logs when undecrypted Events content are mapped to Content model.

Screenshots / GIFs

Tests

• Run the app and send encrypted message after discarding the session.

Tested devices

• Physical
• Emulator
• OS version(s):

Checklist

• Changes has been tested on an Android device or Android emulator with API 21
• UI change has been tested on both light and dark themes
• Accessibility has been taken into account. See https://github.com/element-hq/element-android/blob/develop/CONTRIBUTING.md#accessibility
• Pull request is based on the develop branch
• Pull request includes a new file under ./changelog.d. See https://github.com/element-hq/element-android/blob/develop/CONTRIBUTING.md#changelog
• Pull request includes screenshots or videos if containing UI changes
• Pull request includes a sign off
• You've made a self review of your PR
• If you have modified the screen flow, or added new screens to the application, you have updated the test UiAllScreensSanityTest.allScreensTest()

[BillCarsonFr]

LGTM

[BillCarsonFr]

ouch :/

[bmarty]

There is a failing test Mixed content event should be detected, I am looking at it.