Check get result against false when removing file from cache

[VicDeo]

Description

This is critical for unit tests to pass with PHP 7.4

Related Issue

https://github.com/owncloud/enterprise/issues/3967

Motivation and Context

Many unit tests are failing for PHP 7.4
Before https://drone.owncloud.com/owncloud/core/24348/24/9:

Tests: 9984, Assertions: 57374, Errors: 153, Failures: 1, Skipped: 79.

After https://drone.owncloud.com/owncloud/core/24349/24/9

 Tests: 9984, Assertions: 57729, Errors: 44, Failures: 1, Skipped: 79.

How Has This Been Tested?

By CI

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Database schema changes (next release will require increase of minor version instead of patch)
• Breaking change (fix or feature that would cause existing functionality to change)
• Technical debt
• Tests only (no source changes)

Checklist:

• Code changes
• Unit tests added
• Acceptance tests added
• Documentation ticket raised:
• Changelog item, see TEMPLATE

[update-docs]

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would create a changelog item based on your changes.

[codecov]

Codecov Report

Merging #37281 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master   #37281   +/-   ##
=========================================
  Coverage     64.52%   64.52%           
- Complexity    19155    19156    +1     
=========================================
  Files          1266     1266           
  Lines         74912    74913    +1     
  Branches       1331     1331           
=========================================
+ Hits          48340    48341    +1     
  Misses        26180    26180           
  Partials        392      392           

Flag	Coverage Δ	Complexity Δ
#javascript	54.14% <ø> (ø)	0.00 <ø> (ø)
#phpunit	65.68% <100.00%> (+<0.01%)	19156.00 <0.00> (+1.00)

Impacted Files	Coverage Δ	Complexity Δ
lib/private/Files/Cache/Cache.php	97.64% <100.00%> (+<0.01%)	107.00 <0.00> (+1.00)

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