Unable to submit Temporary Target Cancel - requests valid top and bottom range values

[Nightfoxy]

Describe the bug
I try to set a Temporary Target Cancel action in the care portal, but when I submit, I am prompted to "Please enter a valid value for both top and bottom target to save a Temporary Target" and the submission is not completed. For the Temporary Target Cancel, there are no top and bottom value fields nor should there be.

To Reproduce
Steps to reproduce the behavior:

1. Go to '+' (top right, with careportal enabled)
2. Select 'Temporary Target Cancel' as the Event Type
3. Click 'Submit Form'
4. See error: 'Please enter a valid value for both top and bottom target to save a Temporary Target'

Expected behavior
Select Temporary Target Cancel and submit with no errors.

Screenshots
If applicable, add screenshots to help explain your problem

Your setup information

• What version of Nightscout 0.12.3
• What type of CGM, and how do you get your data there? Dexcom G6 using the Dexcom app and Brdige
• Is your issue specific to a browser (Firefox/Safari/Chrome?) or a device (Android phone, etc.)? No. Replicated on Chrome Desktop and on Android Chrome as well as MS Edge

Additional context
Add any other context about the problem here.

[unsoluble]

Is looking like this was probably an unintended side-effect of #4812.