Some operations within a control callback, in particular setting bounds
in a heuristic callback, are not possible to do on variables that
have been taken out by presolve. An exception of this type is thrown,
if such an operation is attempted. Possible ways to avoid this
exception are to avoid the operation on presolved variables,
to use the method
IloCplex::protectVariables
to protect the variables from being taken out by presolve,
or to turn off presolve.
This method must be called to free up the memory used by the exception
when the invoking exception object is no longer needed.
This methods copies the variables that caused the invoking exception
into the array vars.
