Avoid calling preg_replace on array content

[IProSoft]

In our company we are using some extensions and patches to CRM Core that alter CRM_Core_BAO_MessageTemplate::sendTemplate params, adding an array of additional params like event info.

After our changes \Civi\Core\Event\GenericHookEvent $e->content contains one item that is not string, but array so calling preg_replace_callback on all items removes our data.

This change won't affect any of [uk.co.vedaconsulting.mosaico] functions but will save lot work in our side.

I will be very grateful if you implement this change

[mattwire]

@IProSoft Please can you add a (1 or 2 line) comment to the code to explain why so that a future developer understands and does not undo the changes.