xmb: Prevent crashes when resizing to a tiny window.

If the user resized their RetroArch window while using xmb it would
initiate a context_reset to scale xmb. When the window is too small
this would result in invalid pointers and a crash in the video driver.

This makes it so that when the window is too small it will skip the
context_reset and not crash. The window at this size is not really
useful to scale anyways.

Fixes libretro#8260

menu/drivers/xmb.c

@@ -3156,7 +3156,7 @@ static void xmb_render(void *data, bool is_idle)
 
    scale_factor = (settings->uints.menu_xmb_scale_factor * (float)width) / (1920.0 * 100);
 
-   if (scale_factor != xmb->previous_scale_factor)
+   if (scale_factor >= 0.1f && scale_factor != xmb->previous_scale_factor)
       xmb_context_reset_internal(xmb, video_driver_is_threaded(),
             false);