[PHP7.4] Fix array access in FederatedShareProvider and Storage/DAV

[VicDeo]

Description

check array key existence before accessing it

Related Issue

• Fixes PHP 7.4 reports "Trying to access array offset" messages #37303

Motivation and Context

Clean log file

How Has This Been Tested?

CI
search for Trying to access array offset on value of type in
https://drone.owncloud.com/owncloud/core/24446/36/8
and
https://drone.owncloud.com/owncloud/core/24446/127/18

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

[mmattel]

Adding @phil-davis as he is the author of the referenced issue

[phil-davis]

Adding @phil-davis as he is the author of the referenced issue

yep, I am aware of this. I will review when @VicDeo gets the code finalized. writes the description and adds a changelog (if needed)

[phil-davis]

LGTM if CI is happy.

[codecov]

Codecov Report

Merging #37311 into master will decrease coverage by 0.00%.
The diff coverage is 88.88%.

@@             Coverage Diff              @@
##             master   #37311      +/-   ##
============================================
- Coverage     64.53%   64.53%   -0.01%     
- Complexity    19166    19167       +1     
============================================
  Files          1266     1266              
  Lines         74952    74957       +5     
  Branches       1331     1331              
============================================
+ Hits          48372    48373       +1     
- Misses        26188    26192       +4     
  Partials        392      392              

Flag	Coverage Δ	Complexity Δ
#javascript	54.14% <ø> (ø)	0.00 <ø> (ø)
#phpunit	65.69% <88.88%> (-0.01%)	19167.00 <0.00> (+1.00)	⬇️

Impacted Files	Coverage Δ	Complexity Δ
...ederatedfilesharing/lib/FederatedShareProvider.php	62.60% <87.50%> (+0.18%)	89.00 <0.00> (+1.00)
lib/private/Files/Storage/DAV.php	78.16% <100.00%> (-0.62%)	0.00 <0.00> (ø)

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