Found while investigating T359992.

Steps to replicate the issue (include links if applicable):

• Select exactly 3 task types in the task type topic selector
• Uncheck quickly the 3 task types
• Observe task counter in the footer of the dialog

What happens?:
The task counter is 1.

What should have happened instead?:

The task counter should be 0 since there are no task types selected.

Software version (on Special:Version page; skip for WMF-hosted wikis like Wikipedia):

Other information (browser name/version, screenshots, etc.):

Note: NewcomerTasksStore.fetchTasks is always adding the preloadedFirstTask to the computing of the task count after a request is made. While that may be correct for some requests where the enabled filters at the time of loading the page exactly match the ones requested, it is wrong for all requests where there are filter differences.