nlopt: fix tests failing when luksan solvers are disabled

[bengsparks]

There is an off-by-one error in the test/CMakeLists.txt that causes the tests to attempt to run disabled Luksan solver code, which in turn causes the test suite to fail:

Optimizing Rosenbrock function (2 dims) using Preconditioned truncated Newton with restarting (local, derivative-based) algorithm
lower bounds at lb = [ -2 -2]
upper bounds at ub = [ 2 2]
Starting guess x = [ 0.629447 0.811584]
Starting function value = 17.3914
ERROR - attempting to use NLOPT_LD_TNEWTON*, but Luksan code disabled
finished after 1.4e-05 seconds.
return code -2 from nlopt_minimize

      Start 59: testopt_algo19_obj1
52/77 Test #57: testopt_algo18_obj1 ..............***Failed    0.01 sec
testopt: error in nlopt_minimize
-----------------------------------------------------------
Optimizing McCormic function (2 dims) using Preconditioned truncated Newton with restarting (local, derivative-based) algorithm
lower bounds at lb = [ -1.5 -3]
upper bounds at ub = [ 4 4]
Starting guess x = [ 2.11549 1.92027]
Starting function value = 1.88587
ERROR - attempting to use NLOPT_LD_TNEWTON*, but Luksan code disabled
finished after 1.7e-05 seconds.
return code -2 from nlopt_minimize

97% tests passed, 2 tests failed out of 63