Return PixelAccess from first load of ICO and IPTC images

[radarhere]

ICO and IPTC load() return None the first time processing data, leading to the following assertions failing.

from PIL import Image
with Image.open("Tests/images/hopper.png") as im:
    im.save("out.ico", sizes=[(32, 32), (64, 64)])
with Image.open("out.ico") as reloaded:
    reloaded.size = (32, 32)
    assert reloaded.load() is not None

and

import io
from PIL import Image
f = io.BytesIO(
    b"\x1c\x03<\x00\x02\x01\x00\x1c\x03x\x00\x01\x01\x1c\x03\x14\x00\x01\x01"
    b"\x1c\x03\x1e\x00\x01\x01\x1c\x08\n\x00\x01\x00"
)
with Image.open(f) as im:
    assert im.load() is not None

This fixes that, and also prevents repeated IPTC load() calls from regenerating the C image instance.