prep_match_table fails without species information

[mhpob]

prep_match_table fails on ACT data after update to accommodate networks that provide species info.

Error:

Error in [.data.table(extract, , .(detections = .N), by = c("trackercode", : Column or expression 2 of 'by' or 'keyby' is type 'NULL' which is not currently supported. If you have a compelling use case, please add it to Rdatatable/data.table#1597. As a workaround, consider converting the column to a supported type, e.g. by=sapply(list_col, toString), whilst taking care to maintain distinctness in the process.

Failed matos tests: https://github.com/mhpob/matos/actions/runs/12434501188/job/34718325493