Make it possible to have a Variable not belonging to any LinearSpec.

src/libs/linprog/LinearSpec.cpp

@@ -93,6 +93,9 @@ LinearSpec::AddVariable(Variable* variable)
 	if (!fVariables.AddItem(variable))
 		return false;
 
+	if (variable->fLS == NULL)
+		variable->fLS = this;
+
 	if (!fSolver->VariableAdded(variable)) {
 		fVariables.RemoveItem(variable);
 		return false;

src/libs/linprog/Variable.cpp

@@ -325,6 +325,7 @@ Variable::RemoveReference()
  */
 Variable::~Variable()
 {
-	fLS->RemoveVariable(this, false);
+	if (fLS)
+		fLS->RemoveVariable(this, false);
 }