Fix state_at for extra path variables
Calling state_at() on a path variable that the user defined/added in the path_variables property of OptimizationProblem resulted in an Exception that the symbol could not be found. This commit fixes this issue.
Calling state_at() on a path variable that the user defined/added in the path_variables property of OptimizationProblem resulted in an Exception that the symbol could not be found. This commit fixes this issue.