Link checker: don't send an RO report if no error
Link checker: don't send an RO report if no error

When checking RO links of all data sources, don't send emails for
data sources with no errors.

(You will still get an email if you're only checking one data
source that has no errors.)

au-research/ANDS-Registry-Core,au-research/ANDS-Registry-Core,au-research/ANDS-Registry-Core,au-research/ANDS-Registry-Core,au-research/ANDS-Registry-Core