OnDiskBitmap: Fix memory corruption when using palette image
OnDiskBitmap: Fix memory corruption when using palette image

The number of palette entries set was accidentally 4x too much,
because the wrong looping variable was used.

adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython