weight for SRV records should be at least 1 (#3931)

Automatically submitted.

plugin/backend_lookup.go

@@ -185,6 +185,10 @@ func SRV(ctx context.Context, b ServiceBackend, zone string, state request.Reque
 			w1 *= float64(serv.Weight)
 		}
 		weight := uint16(math.Floor(w1))
+		// weight should be at least 1
+		if weight == 0 {
+			weight = 1
+		}
 
 		what, ip := serv.HostType()