Draft : also clear draft when composer is blank

[ganfra]

Type of change

• Feature
• Bugfix
• Technical
• Other :

Content

At the moment, draft was cleared only when getting the draft, which is not enought.
If the app is put in bakground while you have a text in the composer, then the draft will be saved.
If you then send the message, and then close the room, the draft will remain and will reappear when re-opening the room.

So, this will now take care to clear the draft when composer is blank too.

Motivation and context

Screenshots / GIFs

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

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[codecov]

Codecov Report

Attention: Patch coverage is 30.00000% with 7 lines in your changes missing coverage. Please review.

Project coverage is 75.95%. Comparing base (aa0a6ce) to head (3a610e6).
Report is 6 commits behind head on develop.

Files	Patch %	Lines
...messages/impl/draft/DefaultComposerDraftService.kt	0.00%	6 Missing ⚠️
...s/impl/messagecomposer/MessageComposerPresenter.kt	75.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3115      +/-   ##
===========================================
- Coverage    75.95%   75.95%   -0.01%     
===========================================
  Files         1636     1636              
  Lines        38608    38612       +4     
  Branches      7462     7463       +1     
===========================================
+ Hits         29326    29327       +1     
- Misses        5393     5396       +3     
  Partials      3889     3889              

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[bmarty]

LGTM, thanks!

[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