Various changes suggested by cppcheck

- remove unused variables
- reduce the scope where it makes sense
- correct limits (did you know that strcat()'s last parameter does not
  include the \0 that is always added?)
- set some free()'d pointers to NULL

Source/Core/VideoBackends/D3D/main.cpp

@@ -154,8 +154,6 @@ bool VideoBackend::Initialize(void *&window_handle)
 
 	frameCount = 0;
 
-	const SCoreStartupParameter& core_params = SConfig::GetInstance().m_LocalCoreStartupParameter;
-
 	g_Config.Load((File::GetUserPath(D_CONFIG_IDX) + "gfx_dx11.ini").c_str());
 	g_Config.GameIniLoad();
 	g_Config.UpdateProjectionHack();