OR… you can insert
next if number < 1
… into the iterator block that writes the report lines:
total = 0
matches.each {|definition|
number = definition.count_used_instances
next if number < 1
total += number
attribute = definition.get_attribute(dictionary_name, 'lenz').to_l
height = Sketchup.format_length( attribute )
@report << format( DATALINE, definition.name, height, number )
}