xen: Fix unconditional freeing in xenDaemonListDefinedDomains()

Commit 790f0b3057 causes the contents of
the names array to be freed even on success, resulting in no listing of
defined but inactive Xen domains.

Spotted by Jim Fehlig

src/xen/xend_internal.c

@@ -4696,12 +4696,17 @@ xenDaemonListDefinedDomains(virConnectPtr conn, char **const names, int maxnames
             break;
     }
 
+cleanup:
+    sexpr_free(root);
+    return(ret);
+
 error:
     for (i = 0; i < ret; ++i)
         VIR_FREE(names[i]);
 
-    sexpr_free(root);
-    return(ret);
+    ret = -1;
+
+    goto cleanup;
 }
 
 /**