py/emitnative: Ensure encoding to load prelude_offset doesn't change sz.
py/emitnative: Ensure encoding to load prelude_offset doesn't change sz.

Based on change made by Graham Sanderson.

Signed-off-by: Damien George <99e6b749acbfbe2a596df99e91d24d6e1fdbee00@micropython.org>

adafruit/circuitpython,henriknelson/micropython,adafruit/circuitpython,henriknelson/micropython,bvernoux/micropython,adafruit/circuitpython,adafruit/circuitpython,bvernoux/micropython,adafruit/circuitpython,henriknelson/micropython,bvernoux/micropython,adafruit/circuitpython,henriknelson/micropython,bvernoux/micropython,henriknelson/micropython,bvernoux/micropython