Floating point error sometimes makes the variance -\epsilon

Docker/parse_logs

@@ -317,7 +317,7 @@ sub statstr {
     my $data = $_[0];
     if (defined $data->[1]) {
         my $mean = $data->[0];
-        my $stddev = sqrt($data->[1]);
+        my $stddev = $data->[1] > 0 ? sqrt($data->[1]) : 0;
         return "$mean ± $stddev";
     } elsif (defined $data->[0]) {
         return $data->[0];