Guard against php8.0 ArgumentCountError

[engahmeds3ed]

Fixes the following error:

2022-06-21T00:00:13+00:00 CRITICAL Uncaught ArgumentCountError: array_merge() does not accept unknown named parameters in /home/XXX/public_html/wp-content/plugins/imagify/inc/classes/class-imagify-custom-folders.php:847

that's php8.0 new feature which called Named Parameters which means that we can pass arguments to any function and give them names, something like:

//PHP function usage
function str_contains(string $haystack, string $needle): bool {}

//how to use it with the new feature (named parameters)
str_contains(haystack: 'FooBar', needle: 'Foo');

back to our code, in the following line:

imagify-plugin/inc/classes/class-imagify-custom-folders.php

Line 847 in 5971929

$files_from_db = call_user_func_array( 'array_merge', $files_from_db );

this variable $files_from_db is associative array (array with keys and values) and we are trying to merge all values (which are arrays)
This is because call_user_func_array will interpret the top-level array keys as parameter names to be passed into the array_merge, and these keys will not match the function arguments.
the solution here is just to get the array_values before passing it to call_user_func_array to be like

$files_from_db = call_user_func_array( 'array_merge', array_values( $files_from_db ) );

I wasn't able to see that in the test environment but this PR should fix this error.