.ini files need to be opened for read/write access when writing/updating

This happened to work before commit d49134e6 since iniReadFile()
didn't return false upon any read error, so File.iniSetAllObjects() didn't
realize that the read of (any) existing file contents had failed (because the
file was open write-only).

This explains why the *.avatars.ini files were pretty much blank as of late
and no networked message posters were having their avatars displayed.
Reported by Codefenix (thank you).

Add a print/log line to tell us how many avatars were parsed, just for extra
traceability of this script and any potential failure cause.