Fix a bug in mj_recompile.

The qposadr_ and dofadr_ variables of the joints were not being reset to -1 when a joint is copied. This could lead to errors when calling mj_recompile after attaching a compiled spec.

PiperOrigin-RevId: 686152004
Change-Id: I9e058089ce87ea0d8e51a7f43475bc48c6527a26

src/user/user_objects.cc

@@ -1951,6 +1951,8 @@ mjCJoint& mjCJoint::operator=(const mjCJoint& other) {
     this->spec = other.spec;
     *static_cast<mjCJoint_*>(this) = static_cast<const mjCJoint_&>(other);
     *static_cast<mjsJoint*>(this) = static_cast<const mjsJoint&>(other);
+    qposadr_ = -1;
+    dofadr_ = -1;
   }
   PointToLocal();
   return *this;