Fix crash when aspectRatio is null.

[bmarty]

Content

Rule number one: never use !! or you will provoke the wrath of the Kotlin God :).
This PR fixes a crash when the aspectRatio is unknown (and so null).
Add screenshot to cover this case, but strangely the preview was rendered before the fix (not correctly but without crashing).

Motivation and context

Closes #3552 (confirmed it fixes the issue)

Screenshots / GIFs

Before: crash
After:

Tests

• Step 1
• Step 2
• Step ...

Tested devices

• Physical
• Emulator
• OS version(s):

Checklist

• Changes have been tested on an Android device or Android emulator with API 23
• UI change has been tested on both light and dark themes
• Accessibility has been taken into account. See https://github.com/element-hq/element-x-android/blob/develop/CONTRIBUTING.md#accessibility
• Pull request is based on the develop branch
• Pull request title will be used in the release note, it clearly define what will change for the user
• 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

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[github-actions]

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[codecov]

Codecov Report

Attention: Patch coverage is 88.88889% with 1 line in your changes missing coverage. Please review.

Project coverage is 82.68%. Comparing base (148da7b) to head (6a8086c).
Report is 3 commits behind head on develop.

Files with missing lines	Patch %	Lines
...meline/components/event/TimelineItemStickerView.kt	50.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #3561   +/-   ##
========================================
  Coverage    82.68%   82.68%           
========================================
  Files         1732     1732           
  Lines        40970    40974    +4     
  Branches      4962     4964    +2     
========================================
+ Hits         33874    33879    +5     
  Misses        5341     5341           
+ Partials      1755     1754    -1     

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[jmartinesp]

I humbly ask forgiveness from the mighty Kotlin God 🙏 .

Thanks for fixing the issue!