fix: bug when match functions used in model.conf (#154)

- add: load match functions to function map in method m_enforce()
Fix: #140

Signed-off-by: noob20000405 <vincent4869code@gmail.com>

casbin/enforcer.cpp

@@ -39,6 +39,7 @@ namespace casbin {
 bool Enforcer::m_enforce(const std::string& matcher, Scope scope) {
     m_func_map.scope = scope;
     m_func_map.func_list.clear();
+    m_func_map.LoadFunctionMap();
 
     if(!m_enabled)
         return true;