V4S: Error in Calendar Availability Label when Null Desired Volunteers

[jessingrass]

Reproduce:

In an org with websites enabled, an active campaign, and upcoming shifts on a job:

1. Set up a job with a shift in the future
2. DO NOT SET DESIRED VOLUNTEERS NUMBER for the shift
3. Go to the job calendar on the website for the job EXPECTED: The volunteer shift will display without the word "full" in the calendar ACTUAL: The volunteer shift displays with the word "full" in the calendar.

Please see the screenshots of the job site listing vs. the way that listing appears in the calendar.

[davidhabib]

**lurch: add

[LurchTheButler]

Tracking W-022776