printer json BUGFIX escaped chars in opaque value

Fixes #2034
diff --git a/src/printer_json.c b/src/printer_json.c
index d73adca..98671d9 100644
--- a/src/printer_json.c
+++ b/src/printer_json.c
@@ -908,7 +908,7 @@
             ly_print_(pctx->out, "%s", node->value);
         } else {
             /* string or a large number */
-            ly_print_(pctx->out, "\"%s\"", node->value);
+            json_print_string(pctx->out, node->value);
         }
         LEVEL_PRINTED;