Fix user_has_octave_forge_package

Packages are no longer autoloaded, so testing whether they are "Loaded" does
not work in all cases.

The function now ensures that the package is loaded.

(cherry picked from commit 7cbac0c9)

matlab/optimization/dynare_minimize_objective.m

@@ -135,11 +135,7 @@ switch minimizer_algorithm
         simulated_annealing(objective_function,start_par_value,sa_options,LB,UB,varargin{:});
   case 3
     if isoctave && ~user_has_octave_forge_package('optim')
-        try
-            pkg load optim
-        catch
-            error('Optimization algorithm 3 requires the optim package')
-        end
+        error('Optimization algorithm 3 requires the optim package')
     elseif ~isoctave && ~user_has_matlab_license('optimization_toolbox')
         error('Optimization algorithm 3 requires the Optimization Toolbox')
     end

matlab/user_has_octave_forge_package.m

@@ -20,4 +20,11 @@ function [hasPackage] = user_has_octave_forge_package(package)
 
 [desc,flag] = pkg('describe', package);
 
-hasPackage = isequal(flag{1,1}, 'Loaded');
+if isequal(flag{1,1}, 'Not installed')
+    hasPackage = 0;
+else
+    if isequal(flag{1,1}, 'Not loaded')
+        pkg('load', package);
+    end
+    hasPackage = 1;
+end