module: Make make_config() pure virtual

It is important to implement this method in derived classes. When we
provided default implementation returning NULL, introducing new methods
might leave this method not implemented without a compiler error.

Signed-off-by: Simon Rozman <simon@rozman.si>

CredWrite/Main.cpp

@@ -23,7 +23,9 @@
 using namespace std;
 using namespace winstd;
 
-eap::module g_module;
+class module_dummy : public eap::module {
+    virtual eap::config_method* make_config() { return nullptr; }
+} g_module;
 
 
 static int CredWrite()

CredWrite/StdAfx.h

@@ -20,6 +20,7 @@
 
 #pragma once
 
+#include "../lib/EAPBase/include/Config.h"
 #include "../lib/EAPBase/include/Credentials.h"
 #include "../lib/EAPBase/include/Module.h"