wined3d: Shaders will never have a NULL function.

[wine] / dlls / xinput1_3 / xinput1_3.spec

@ stub XInputEnable #(long)
@ stub XInputSetState #(long ptr)
@ stdcall XInputGetState(long ptr)
@ stub XInputGetKeystroke #(long long ptr)
@ stdcall XInputGetCapabilities(long long ptr)
@ stub XInputGetDSoundAudioDeviceGuids #(long ptr ptr)
@ stub XInputGetBatteryInformation