Fix set (extra) find ret value

src/set/extra.c

@@ -28,7 +28,7 @@ _Bool libcdsb_vset_find(val_t* x, set_t* s, const void* v, vtype t, _Bool cut) {
 
         c = (cmp < 0) ? c->right : c->left;
     }
-    return rbnode_empty;
+    return false;
 }