py/objstr: Remove unnecessary check for positive splits variable.
py/objstr: Remove unnecessary check for positive splits variable.

At this point in the code the variable "splits" is guaranteed to be
positive due to the check for "splits == 0" above it.

tobbad/micropython,adafruit/circuitpython,pfalcon/micropython,selste/micropython,dmazzella/micropython,trezor/micropython,adafruit/circuitpython,tralamazza/micropython,tobbad/micropython,pozetroninc/micropython,adafruit/micropython,bvernoux/micropython,tralamazza/micropython,adafruit/micropython,dmazzella/micropython,pfalcon/micropython,adafruit/micropython,henriknelson/micropython,pfalcon/micropython,selste/micropython,tobbad/micropython,selste/micropython,dmazzella/micropython,ryannathans/micropython,tralamazza/micropython,ryannathans/micropython,selste/micropython,pramasoul/micropython,MrSurly/micropython,bvernoux/micropython,swegener/micropython,kerneltask/micropython,pramasoul/micropython,swegener/micropython,adafruit/circuitpython,bvernoux/micropython,trezor/micropython,pramasoul/micropython,swegener/micropython,swegener/micropython,tobbad/micropython,pozetroninc/micropython,trezor/micropython,selste/micropython,MrSurly/micropython,MrSurly/micropython,pozetroninc/micropython,adafruit/circuitpython,pozetroninc/micropython,henriknelson/micropython,henriknelson/micropython,pfalcon/micropython,pramasoul/micropython,ryannathans/micropython,adafruit/micropython,bvernoux/micropython,ryannathans/micropython,kerneltask/micropython,adafruit/circuitpython,tralamazza/micropython,MrSurly/micropython,tobbad/micropython,trezor/micropython,dmazzella/micropython,kerneltask/micropython,pramasoul/micropython,MrSurly/micropython,henriknelson/micropython,adafruit/micropython,adafruit/circuitpython,pfalcon/micropython,pozetroninc/micropython,trezor/micropython,kerneltask/micropython,ryannathans/micropython,kerneltask/micropython,swegener/micropython,henriknelson/micropython,bvernoux/micropython