Do not use fast lookup for frames.

Fast lookup is not possible since mjOBJ_FRAME > mjNOBJECT, which is the size of the objects maps used for the search.

Fixes #2328.

PiperOrigin-RevId: 712479460
Change-Id: I7bcfa75ff8a1e288183d60ed4a44cab5bc6f4173

src/user/user_api.cc

@@ -614,7 +614,7 @@ mjsBody* mjs_findBody(mjSpec* s, const char* name) {
 // find element in spec by name
 mjsElement* mjs_findElement(mjSpec* s, mjtObj type, const char* name) {
   mjCModel* model = static_cast<mjCModel*>(s->element);
-  if (model->IsCompiled()) {
+  if (model->IsCompiled() && type != mjOBJ_FRAME) {
     return model->FindObject(type, std::string(name));  // fast lookup
   }
   switch (type) {

test/user/user_api_test.cc

@@ -1014,6 +1014,9 @@ TEST_F(MujocoTest, AttachDifferent) {
   mjModel* m_attached = mj_compile(parent, 0);
   EXPECT_THAT(m_attached, NotNull());
 
+  // check frame is present
+  EXPECT_THAT(mjs_findFrame(parent, "frame"), NotNull());
+
   // check full name stored in mjModel
   EXPECT_STREQ(mj_id2name(m_attached, mjOBJ_BODY, 2), "attached-body-1");