Minimum activities for a reading page is 1 not 0

[bnmnetp]

We count 1 activity as just opening the page. So the minimum number of activities should never be 0, it should always be at least 1.

[bnmnetp]

All of the Activity Counts as shown in the add readings panel are off by 1. I'm using the PreTeXt sample-book (PTXSB) for testing. There may be different behavior when using one of our older books that is still written in RST.