The agents aren't unbinding as frequently as they should

## Description

if they are already bound, the don't unbind 


[the fix is in my draft PR](https://github.com/simularium/binding-sim-edu/pull/175/files#diff-095f6eed2b1526d36c8d747fcab8fbbd1ce0c91446776bc4ae640eac943e9cfd)