[stable31] 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 6 lines in your changes missing coverage. Please review.

Project coverage is 30.80%. Comparing base (4cca650) to head (d91605a).
Report is 3 commits behind head on stable31.

Files with missing lines	Patch %	Lines
src/views/ActivityAppFeed.vue	0.00%	6 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           stable31    #1964      +/-   ##
============================================
- Coverage     30.89%   30.80%   -0.10%     
============================================
  Files            43       43              
  Lines          1615     1620       +5     
  Branches        110      110              
============================================
  Hits            499      499              
- Misses         1090     1095       +5     
  Partials         26       26              

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[Antreesy]

/compile /