Prevent undefined array reference error

Following error encountered when trying to print a latency summary, in a rare situation where all of the results were strikes:

    Can't use an undefined value as an ARRAY reference at sqm-autorate.pl line 1253.

Prevent this error by checking that the valid ping array references are defined before trying to dereference them.

sqm-autorate.pl

@@ -1250,6 +1250,11 @@ sub print_latency_results_summary {
 		return;
 	}
 
+	if (!defined($valid_pings_ul_ref) || !defined($valid_pings_dl_ref)) {
+		&output(0, "LATENCY SUMMARY: No valid results!");
+		return;
+	}
+
 	my @valid_pings_ul = @{$valid_pings_ul_ref};
 	my @valid_pings_dl = @{$valid_pings_dl_ref};