Fix wrong results returned by isEnabled

When language filter plugin is disabled and language filter is enabled in code using JFactory::getApplication()->setLanguageFilter(true) calling JLanguageAssociations->isEnabled causes notices and fatal errors and returns wrong result if item associations are in fact disabled.

What happens is that JPluginHelper::getPlugin returns empty array when certain plugin is disabled and since there is no params to be passed to JRegistry and $enabled gets default value.
Missing object property "language".
[#32862] Removed // comments from bootstrap css.

The // comments are not intended to be present in the css files.  They are
only present in the .less files to identify changes from standard bootstrap.
Using "joomla.content.icons" JLayout for article and feature view
Adding cy_GB (Welsh) language to installation
Add link to coding standards to contributing.md
Close #3593
Merge pull request #3584 from pjwiseman/32862

[#32862] Removed // comments from bootstrap css.
Several CSS fixes
[bug] [33653] Array to string conversion notice in mod_articles_category with PHP 5.4+ Strict
Close #3595
Merge pull request #3594 from roland-d/cssfixes

[#33721] Several CSS fixes
[Fix][#33037] Email Cloaking causes slower page loading in Firefox (Fix
# 2716)
Merge pull request #3177 from klas/patch-5

Fix wrong results returned by isEnabled
Merge pull request #3136 from Bakual/AddIconsLayout

Using the "joomla.content.icons" JLayout for article and feature view
[Fix][#32894] Nesting issue: beez3/catergory/blog.php [Fix #1952] Thanks
isamrx
[#33150] Use data-direction attribute to update direction (Fix #2797)
Codestyle, closes #3600
Update 3.2 --> 3.3
Close #3601
Protostar template does not highlight com_search results
Codestyle
[bug] [33732] Removed unnecessary 'if' ternary
Close #3596