esp8266/rtc: Set RTC user memory length to 0 on first boot.
esp8266/rtc: Set RTC user memory length to 0 on first boot.

So that RTC.memory() returns b'' on power up if it was never set.

Fixes issue #2138.

redbear/micropython,Timmenem/micropython,kerneltask/micropython,mhoffma/micropython,jmarcelino/pycom-micropython,hiway/micropython,HenrikSolver/micropython,adafruit/circuitpython,toolmacher/micropython,selste/micropython,AriZuu/micropython,deshipu/micropython,dxxb/micropython,swegener/micropython,adafruit/micropython,dmazzella/micropython,micropython/micropython-esp32,swegener/micropython,matthewelse/micropython,Peetz0r/micropython-esp32,MrSurly/micropython,matthewelse/micropython,adafruit/circuitpython,MrSurly/micropython,bvernoux/micropython,ryannathans/micropython,mhoffma/micropython,adafruit/micropython,alex-march/micropython,infinnovation/micropython,toolmacher/micropython,torwag/micropython,pfalcon/micropython,dmazzella/micropython,mhoffma/micropython,ryannathans/micropython,tuc-osg/micropython,turbinenreiter/micropython,toolmacher/micropython,hosaka/micropython,Timmenem/micropython,ryannathans/micropython,lowRISC/micropython,bvernoux/micropython,micropython/micropython-esp32,dinau/micropython,ryannathans/micropython,puuu/micropython,MrSurly/micropython,dxxb/micropython,PappaPeppar/micropython,blazewicz/micropython,Timmenem/micropython,ganshun666/micropython,HenrikSolver/micropython,matthewelse/micropython,tobbad/micropython,hiway/micropython,pozetroninc/micropython,dmazzella/micropython,TDAbboud/micropython,jmarcelino/pycom-micropython,infinnovation/micropython,SHA2017-badge/micropython-esp32,SHA2017-badge/micropython-esp32,PappaPeppar/micropython,pozetroninc/micropython,oopy/micropython,adafruit/micropython,torwag/micropython,Peetz0r/micropython-esp32,dinau/micropython,mhoffma/micropython,pfalcon/micropython,tralamazza/micropython,dxxb/micropython,selste/micropython,dinau/micropython,redbear/micropython,micropython/micropython-esp32,dinau/micropython,alex-robbins/micropython,pramasoul/micropython,torwag/micropython,tuc-osg/micropython,ganshun666/micropython,lowRISC/micropython,alex-march/micropython,redbear/micropython,toolmacher/micropython,tobbad/micropython,alex-march/micropython,turbinenreiter/micropython,chrisdearman/micropython,MrSurly/micropython-esp32,pozetroninc/micropython,Peetz0r/micropython-esp32,redbear/micropython,TDAbboud/micropython,henriknelson/micropython,oopy/micropython,chrisdearman/micropython,swegener/micropython,infinnovation/micropython,pozetroninc/micropython,matthewelse/micropython,dinau/micropython,puuu/micropython,TDAbboud/micropython,MrSurly/micropython-esp32,pfalcon/micropython,turbinenreiter/micropython,SHA2017-badge/micropython-esp32,tobbad/micropython,MrSurly/micropython,alex-robbins/micropython,AriZuu/micropython,oopy/micropython,ryannathans/micropython,adafruit/circuitpython,pfalcon/micropython,jmarcelino/pycom-micropython,PappaPeppar/micropython,ganshun666/micropython,emfcamp/micropython,pramasoul/micropython,oopy/micropython,dmazzella/micropython,hiway/micropython,adafruit/circuitpython,AriZuu/micropython,tuc-osg/micropython,emfcamp/micropython,bvernoux/micropython,alex-robbins/micropython,SHA2017-badge/micropython-esp32,kerneltask/micropython,deshipu/micropython,hosaka/micropython,tralamazza/micropython,dxxb/micropython,torwag/micropython,kerneltask/micropython,redbear/micropython,swegener/micropython,jmarcelino/pycom-micropython,cwyark/micropython,torwag/micropython,selste/micropython,lowRISC/micropython,adafruit/circuitpython,selste/micropython,selste/micropython,tuc-osg/micropython,tobbad/micropython,hosaka/micropython,TDAbboud/micropython,pfalcon/micropython,infinnovation/micropython,deshipu/micropython,Timmenem/micropython,turbinenreiter/micropython,turbinenreiter/micropython,mhoffma/micropython,micropython/micropython-esp32,MrSurly/micropython-esp32,trezor/micropython,henriknelson/micropython,infinnovation/micropython,mpalomer/micropython,PappaPeppar/micropython,trezor/micropython,pramasoul/micropython,pramasoul/micropython,kerneltask/micropython,hiway/micropython,trezor/micropython,cwyark/micropython,trezor/micropython,blazewicz/micropython,TDAbboud/micropython,adafruit/circuitpython,ganshun666/micropython,AriZuu/micropython,oopy/micropython,Timmenem/micropython,MrSurly/micropython-esp32,blazewicz/micropython,bvernoux/micropython,chrisdearman/micropython,tobbad/micropython,cwyark/micropython,HenrikSolver/micropython,AriZuu/micropython,mpalomer/micropython,alex-robbins/micropython,mpalomer/micropython,deshipu/micropython,deshipu/micropython,alex-march/micropython,henriknelson/micropython,matthewelse/micropython,HenrikSolver/micropython,Peetz0r/micropython-esp32,ganshun666/micropython,toolmacher/micropython,SHA2017-badge/micropython-esp32,mpalomer/micropython,cwyark/micropython,emfcamp/micropython,PappaPeppar/micropython,cwyark/micropython,henriknelson/micropython,tuc-osg/micropython,MrSurly/micropython,hosaka/micropython,bvernoux/micropython,trezor/micropython,alex-march/micropython,chrisdearman/micropython,matthewelse/micropython,MrSurly/micropython-esp32,puuu/micropython,kerneltask/micropython,lowRISC/micropython,pozetroninc/micropython,micropython/micropython-esp32,HenrikSolver/micropython,chrisdearman/micropython,henriknelson/micropython,tralamazza/micropython,swegener/micropython,lowRISC/micropython,mpalomer/micropython,dxxb/micropython,tralamazza/micropython,hosaka/micropython,emfcamp/micropython,puuu/micropython,adafruit/micropython,emfcamp/micropython,pramasoul/micropython,blazewicz/micropython,blazewicz/micropython,alex-robbins/micropython,adafruit/micropython,puuu/micropython,hiway/micropython,jmarcelino/pycom-micropython,Peetz0r/micropython-esp32