stm32/modusocket: Fix NULL deref when accept() an unbound socket.
stm32/modusocket: Fix NULL deref when accept() an unbound socket.

selste/micropython,tobbad/micropython,pramasoul/micropython,pozetroninc/micropython,pozetroninc/micropython,henriknelson/micropython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,henriknelson/micropython,trezor/micropython,selste/micropython,tobbad/micropython,tobbad/micropython,henriknelson/micropython,trezor/micropython,pramasoul/micropython,henriknelson/micropython,MrSurly/micropython,MrSurly/micropython,MrSurly/micropython,henriknelson/micropython,trezor/micropython,MrSurly/micropython,kerneltask/micropython,pramasoul/micropython,bvernoux/micropython,trezor/micropython,kerneltask/micropython,bvernoux/micropython,bvernoux/micropython,trezor/micropython,pramasoul/micropython,pozetroninc/micropython,pozetroninc/micropython,kerneltask/micropython,pozetroninc/micropython,kerneltask/micropython,adafruit/circuitpython,selste/micropython,tobbad/micropython,MrSurly/micropython,bvernoux/micropython,kerneltask/micropython,selste/micropython,tobbad/micropython,selste/micropython,bvernoux/micropython,adafruit/circuitpython,adafruit/circuitpython,pramasoul/micropython