Fix uninitialized variable error

If you run minetest with valgrind, you'll quickly notice uninitialized jump
depend error messages that point to s_base.cpp:131. This commit fixes those.

src/script/cpp_api/s_base.cpp

@@ -103,6 +103,11 @@ ScriptApiBase::ScriptApiBase()
 	lua_pushstring(m_luastack, porting::getPlatformName());
 	lua_setglobal(m_luastack, "PLATFORM");
 
+	// m_secure gets set to true inside
+	// ScriptApiSecurity::initializeSecurity(), if neccessary.
+	// Default to false otherwise
+	m_secure = false;
+
 	m_server = NULL;
 	m_environment = NULL;
 	m_guiengine = NULL;