py/objdict: Fix optimisation for allocating result in fromkeys.
py/objdict: Fix optimisation for allocating result in fromkeys.

Iterables don't respond to __len__, so call __len__ on the original
argument.

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