Otherwise generates a URL like
In https://github.com/matomo-org/matomo/blob/3.13.1-b2/plugins/CoreHome/angularjs/http404check.js#L29 there will be otherwise
['./additional=plugins/', 'AbTesting', '...'].join(). The
pluginsToWebRootDirCache is only used for that purpose.
This should not fix the referenced issue as a double slash should not cause any issue AFAIK but be still good to make that right. The
$pluginsToWebRootDirCache is only used for that purpose to load these files through http404check