Add error checking in mjs_setFrame.

Also raise error if the frame is not found in the mjCBody copy constructor.

Fixes #2543.

PiperOrigin-RevId: 742624013
Change-Id: I4999b3165c97f8d079412214d027ca7a8dae8cb3

src/xml/xml_native_reader.cc

@@ -3647,7 +3647,9 @@ void mjXReader::Body(XMLElement* section, mjsBody* body, mjsFrame* frame,
         }
       } else {
         // only set frame to existing body
-        mjs_setFrame(child->element, pframe);
+        if (mjs_setFrame(child->element, pframe)) {
+          throw mjXError(elem, mjs_getError(spec));
+        }
       }
     }