Fix: report multiple candidates only if it isn't same table

For some reason, lua table.sort function calls compare function with
arguments being  same tables. This commit just ensures that warning
isn't printed if such thing happens.
2 jobs for multiple-candidates-warn in 4 minutes and 23 seconds (queued for 1 second)
Status Name Job ID Coverage
  Test
passed test #2133

00:04:02

passed test_busybox #2134

00:04:23