Fix potential error if the config could not be loaded

[qzminski]

We have the below exception logged in the Sentry. Unfortunately I could not reproduce this myself. This likely happens when the config file cannot be loaded but I am not able to tell why.

ErrorException: Invalid argument supplied for foreach()
#17 vendor/madeyourday/contao-rocksolid-custom-elements/src/CustomElements.php(460): handleError
#16 vendor/madeyourday/contao-rocksolid-custom-elements/src/CustomElements.php(460): createDca
#15 vendor/madeyourday/contao-rocksolid-custom-elements/src/CustomElements.php(97): onloadCallback
#14 vendor/contao/core-bundle/src/Resources/contao/drivers/DC_Table.php(205): __construct
#13 vendor/contao/core-bundle/src/Resources/contao/classes/Backend.php(407): getBackendModule
#12 vendor/contao/core-bundle/src/Resources/contao/controllers/BackendMain.php(135): run
#11 vendor/contao/core-bundle/src/Controller/BackendController.php(55): mainAction
#10 vendor/symfony/symfony/src/Symfony/Component/HttpKernel/HttpKernel.php(151): handleRaw
#9 vendor/symfony/symfony/src/Symfony/Component/HttpKernel/HttpKernel.php(68): handle
#8 vendor/symfony/symfony/src/Symfony/Component/HttpKernel/Kernel.php(202): handle
#7 vendor/symfony/symfony/src/Symfony/Component/HttpKernel/HttpCache/HttpCache.php(462): forward
#6 vendor/symfony/symfony/src/Symfony/Bundle/FrameworkBundle/HttpCache/HttpCache.php(57): forward
#5 vendor/symfony/symfony/src/Symfony/Component/HttpKernel/HttpCache/HttpCache.php(234): pass
#4 vendor/symfony/symfony/src/Symfony/Component/HttpKernel/HttpCache/HttpCache.php(251): invalidate
#3 vendor/friendsofsymfony/http-cache/src/SymfonyCache/EventDispatchingHttpCache.php(126): invalidate
#2 vendor/symfony/symfony/src/Symfony/Component/HttpKernel/HttpCache/HttpCache.php(177): handle
#1 vendor/friendsofsymfony/http-cache/src/SymfonyCache/EventDispatchingHttpCache.php(98): handle
#0 web/app.php(30): null

Possibly related to #92.

[qzminski]

@ausi can this be merged anytime soon? 😉

[ausi]

Done, released as 2.2.4