Fix logging when logger has no writeExtra method

[phil-davis]

Description

• Correct the call to \is_callable - the first parameter should be an array whose entries are the object concerned and the name of the hoped-for method in the object.
• Add a unit test

Related Issue

• Fixes Error when logging with a logger that has no writeExtra method #37453

How Has This Been Tested?

LoggerWithoutWriteExtraTest.php is a cut-down version of LoggerTest.php that does not have a writeExtra method, and just has the relevant test case.

Without the fix in lib/private/Log.php the test fails:

PHPUnit 8.5.5 by Sebastian Bergmann and contributors.

Runtime:       PHP 7.4.6 with Xdebug 2.9.5
Configuration: /home/phil/git/owncloud/core/tests/phpunit-autotest.xml

E                                                                   1 / 1 (100%)

Time: 110 ms, Memory: 24.00 MB

There was 1 error:

1) Test\LoggerWithoutWriteExtraTest::testExtraFields
call_user_func() expects parameter 1 to be a valid callback, class 'Test\LoggerWithoutWriteExtraTest' does not have a method 'writeExtra'

/home/phil/git/owncloud/core/lib/private/Log.php:398
/home/phil/git/owncloud/core/lib/private/Log.php:247
/home/phil/git/owncloud/core/tests/lib/LoggerWithoutWriteExtraTest.php:59

ERRORS!
Tests: 1, Assertions: 0, Errors: 1.
Makefile:189: recipe for target 'test-php-unit' failed
make: *** [test-php-unit] Error 2

That reproduces the error reported in the issue.

With the fix, the test passes.

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

[codecov]

Codecov Report

Merging #37454 into master will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master   #37454   +/-   ##
=========================================
  Coverage     64.67%   64.67%           
  Complexity    19332    19332           
=========================================
  Files          1277     1277           
  Lines         75521    75521           
  Branches       1331     1331           
=========================================
  Hits          48846    48846           
  Misses        26283    26283           
  Partials        392      392           

Flag	Coverage Δ	Complexity Δ
#javascript	54.14% <ø> (ø)	0.00 <ø> (ø)
#phpunit	65.84% <100.00%> (ø)	19332.00 <0.00> (ø)

Impacted Files	Coverage Δ	Complexity Δ
lib/private/Log.php	82.17% <100.00%> (ø)	49.00 <0.00> (ø)

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[micbar]

Thanks a lot!