[stable29] fix(ActivityAppFeed): handle cases for non-scrollable container

[backportbot]

Backport of #1963

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Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 9 lines in your changes missing coverage. Please review.

Project coverage is 41.87%. Comparing base (5e8f529) to head (dffcb86).
Report is 3 commits behind head on stable29.

Files with missing lines	Patch %	Lines
src/views/ActivityAppFeed.vue	0.00%	9 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           stable29    #1966      +/-   ##
============================================
- Coverage     41.96%   41.87%   -0.09%     
============================================
  Files            43       43              
  Lines          3839     3847       +8     
  Branches        110      110              
============================================
  Hits           1611     1611              
- Misses         2202     2210       +8     
  Partials         26       26              

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[Antreesy]

/compile /