Can not turn off thresholds in Air Alarm UI

Exploit Reports

• I confirm this issue is not an exploit. (Required)

BYOND Version

515.1633

Issue Description

Air Alarms' thresholds can not be turned off by setting them to -1.

What did you expect to happen?

Setting thresholds to -1 should turn them off.

What happened instead?

Setting thresholds to -1 clamps it to 0.

Why is this bad/What are the consequences?

Slight inconvenience over setting the threshold to min/max.

Steps to reproduce the issue.

1. Open an Air Alarm.
2. Go to Thresholds.
3. Set one of them to -1.

When did the problem start happening?

Since TGUI Inputs were introduced.

Extra information

https://github.com/ParadiseSS13/Paradise/blob/521abceae83be85905923cb7253c8eb85a3d6bb7/code/modules/atmospherics/machinery/airalarm.dm#L852

Relevant log output/runtime error

No response