Fix END-IF error message for unexpected END-FOR

[davidjb]

If a template an errant END-FOR command, the current behaviour is to throw an error with the text:

Unexpected END-IF outside of IF statement context

However, the command isn't an END-IF and it isn't within an IF context - the message is just hardcoded to state IF.

This PR changes the outputted error message to report the command name used and corresponding context.

This can be reproduced with a template like this, with just the following text and nothing else:

+++END-FOR person+++

[davidjb]

Closing in lieu of #321. I accidentally created the same PR twice 🫤