Fails to properly decode slim tzdata

[Milan Crha]

	Hello,
a user reported an issue with timezone data in Flatpak on a Linux Mint
machine, showing times one hour ahead when using libical 3.0.9. After
some investigation I realized the org.gnome.Platform provides "slim"
tzdata, which is used on the Linux Mint machine, instead of the "fat"
tzdata, which is on the host system and which can be used on other
systems (I tried on Fedora and Ubuntu). Why it does not use the host
system tzdata I've no idea, but it at least shows a bug in the libical
tzdata parsing.

I filed a bug against the tzdata build for the Flatpak here:
https://gitlab.com/freedesktop-sdk/freedesktop-sdk/-/issues/1202

My helper application is attached. It uses Europe/Berlin timezone. When
I have installed tzdata with `make ZFLAGS='-b fat' install`, then the
time matches, but when I have tzdata installed with
`make ZFLAGS='-b slim' install`, then the time is ahead by one hour.

It seems the problem is with the last change only, at least according
to the diff between the 'good' and the 'bad' time zone component. See
attached tz.diff. 

I do not have any idea what and why the icaltzutil_fetch_timezone()
does, I hope Ken will know what to do.

	Thanks and bye,
	Milan
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