Rules variables are unavailable in template

I have found that Rules variables are unavailable in custom templates. For example, I have defined 2 variables in my Rules component settings - a type User and a type Text variable. I programmatically invoke the Rules component like this:

rules_invoke_component('rules_partner_is_approved', $account, 'A text variable I have defined in my Rules component settings');

That works perfectly when I use the Rules UI to access the variables in various textareas. However, when using a template, $account and the custom text variable never reach the theming layer. I found that Mimemail stores the RulesState $state object in $message['params']['context'] when it is available (this is where the Rules variables can be found). So I have solved this by modifying function mimemail_prepare_message($message) to pass $message['params']['context'] as $variables['context'] to preprocess function(s). I found that $variables['context'] was always an empty array, so I am putting it there. Patch is attached. Needs review and testing.