fix error when debugme is on

[pawelru]

Fix the following error (extract from logs). Note that you have to have debugme switched on.

revdepcheck +-handle event, package chevron +59ms 
Error in handle_event(state, i) : object 'err' not found
Calls: <Anonymous> ... <Anonymous> -> get_debug_levels -> regexpr -> is.factor -> paste0
revdepcheck +-remove 4 workers +2ms 
Execution halted