fix(sub): tolerate a hysteria inbound without hysteriaSettings in the JSON subscription

genHy asserted stream["hysteriaSettings"].(map[string]any) without the comma-ok
form, so a hysteria inbound whose StreamSettings omit the hysteriaSettings key
(a valid, representable shape the raw generator renders fine) panicked and 500ed
the entire JSON subscription. Use comma-ok; the downstream reads already guard
each key, so a nil map degrades gracefully.

internal/sub/json_service.go

@@ -496,7 +496,7 @@ func (s *SubJsonService) genHy(inbound *model.Inbound, newStream map[string]any,
 	}
 
 	_ = json.Unmarshal([]byte(inbound.StreamSettings), &stream)
-	hyStream := stream["hysteriaSettings"].(map[string]any)
+	hyStream, _ := stream["hysteriaSettings"].(map[string]any)
 	outHyStream := map[string]any{
 		"version": int(version),
 		"auth":    client.Auth,