When a text token was running, it wouldn't stop on a $-sign if it wasn't followed with a "[".
This is good.
But when a token was finished and the next char was a $-sign, it would consider it an MFMOpen, even when not followed by a "[".
This is now fixed.
The following cases are now tested and fixed so they don't crash:
* Providing a "]" without there being a mfm token opened.
* Opening a tag without closing. E.g. "$[spin " and "$[spin chocolatine".
* Starting a tag without finishing it. E.g. "$[sp".