String coloring leaks out when not closing text tags

[Gouvernathor]

Somewhat related to #255 (maybe).

This line induces bad coloring, the string it opens leaks out to the following lines.

https://github.com/renpy/renpy/blob/c998b456a17732d5b36068bc1aad38e87fa6c3ff/testcases/game/script.rpy#L169

Notably, replacing it with this lifts the problem $ b = "{b}" # {/b}