CVE-2026-12051 NULL pointer dereference in USB DFU device_next download handler (handle_download)

The USB DFU class implementation in Zephyr's new experimental devicenext USB device stack contains a NULL pointer dereference in handledownload subsys/usb/devicenext/class/usbddfu.c. The handler computes MINsetup-wLength, buf-len and passes buf-data to the image write callback without checking th...