fix: resolve state_unsafe_mutation in getChatVar()

[bangonicdd2]

PR Checklist

• Have you checked if it works normally in all models? Ignore this if it doesn't use models.
• Have you checked if it works normally in all web, local, and node hosted versions? If it doesn't, have you blocked it in those versions?
• Have you added type definitions?

Description

While investigating an issue where {{getvar::A}} didn't work properly in background embedding, I encountered a state_unsafe_mutation error. It appears that modifying the null check operator on the relevant line can resolve this issue. Thank for your time.

[bangonicdd2]

I also found another issue where the order flag in the regex script was not working as intended and included a fix in an additional commit.