moxcms's encode packs tagged elements back to back, so the built-in
sRGB profile embedded in JPEG, TIFF and PSD exports was 634 bytes with
`cprt` at offset 558, where ICC.1 §7.1.2 requires every tagged element
on a 4-byte boundary (stricter readers reject the files). encode now
lays the tag data out again with each element padded, updating the tag
offsets, the size and the profile ID (zeroed, "not computed"); tags
that share data keep sharing it. Reported to moxcms as
awxkee/moxcms#198.
Fixes#1584
7b0164e4e7