Fix metadata breaking json when no searchable is set. Fix #973

Author: cdujeu

core/src/plugins/meta.user/class.UserMetaManager.php

@@ -151,7 +151,7 @@ public function initMeta($accessDriver)
             if (count($searchablesRenderers)) {
                 $metaV .= ',"metaColumnsRenderers":'.json_encode($searchablesRenderers);
             }
-            if (!empty($v) && trim($v) != "{}") {
+            if (!empty($v) && trim($v) != "{}" && !empty($metaV)) {
                 $v = str_replace("}", ", ".$metaV."}", $v);
             } else {
                 $v = "{".$metaV."}";