[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 /