Make mjs_findElement find textures by file name.

This is done if the model is uncompiled and their name is empty.

PiperOrigin-RevId: 772885774
Change-Id: I827d5b679637fa0571cfb0a69833ed688df16304

src/user/user_api.cc

@@ -936,6 +936,8 @@ mjsElement* mjs_findElement(mjSpec* s, mjtObj type, const char* name) {
     case mjOBJ_LIGHT:
     case mjOBJ_FRAME:
       return model->FindTree(model->GetWorld(), type, std::string(name));  // recursive search
+    case mjOBJ_TEXTURE:
+      return model->FindTexture(std::string(name));  // check filename too
     default:
       return model->FindObject(type, std::string(name));  // always available
   }