lib/utils/interrupt_char: Invalidate interrupt char at start up.
lib/utils/interrupt_char: Invalidate interrupt char at start up.

Otherwise mp_interrupt_char will have a value of zero on start up (because
it's in the BSS) and a KeyboardInterrupt may be raised during start up.
For example this can occur if there is a UART attached to the REPL which
sends spurious null bytes when the device turns on.

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