xinput: check for valid function pointers before calling them

CHANGES.md

@@ -40,6 +40,7 @@
 - WINDOWS: Raw input driver now supports new lightgun code.
 - WINDOWS: Use configured OSD/text message color on GDI driver.
 - WINDOWS/XINPUT: Populate XInput VID/PID from DInput so autoconfig doesn't rely solely on joypad names
+- WINDOWS/XINPUT: Fix crash that occurs in some situations with Steam running and a Steam Controller plugged in.
 - WINDOWS: Improve version reporting under System Information.
 - WINDOWS: Support window transparency.
 

input/drivers_joypad/xinput_joypad.c

@@ -475,7 +475,7 @@ static void xinput_joypad_poll(void)
    {
       if (g_xinput_states[i].connected)
       {
-         if (g_XInputGetStateEx(i,
+         if (g_XInputGetStateEx && g_XInputGetStateEx(i,
                   &(g_xinput_states[i].xstate))
                == ERROR_DEVICE_NOT_CONNECTED)
             g_xinput_states[i].connected = false;
@@ -507,6 +507,9 @@ static bool xinput_joypad_rumble(unsigned pad,
    else if (effect == RETRO_RUMBLE_WEAK)
       g_xinput_rumble_states[xuser].wRightMotorSpeed = strength;
 
+   if (!g_XInputSetState)
+      return false;
+
    return (g_XInputSetState(xuser, &g_xinput_rumble_states[xuser])
       == 0);
 }