update-notifier fails on ALL sources if ONE source is bad

[seahen]

Update-notifier doesn't work at all if *one* package source gives a list that can't be parsed. It should still be able to work on packages from *other* sources. After seeing the error in the system tray icon, I ran:

```
$ sudo apt-get update

E: Encountered a section with no Package: header
E: Problem with MergeList /var/lib/apt/lists/adoptopenjdk.jfrog.io_adoptopenjdk_deb_dists_disco_main_binary-amd64_Packages
E: The package lists or status file could not be parsed or opened.
```
apt-get successfully processed all but one of the package lists, so I would have expected update-notifier to do so as well.

I had to manually file this bug, because this error also prevents ubuntu-bug update-notifier from working (see attached).

[seahen (seahen123)]

Although this could in theory be a bug in apt, I was assured at #1848570 that it isn't.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Sebastien Bacher (seb128)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. Unfortunately, we cannot work on this bug because your description didn't include enough information. You may find it helpful to read "How to report bugs effectively" http://www.chiark.greenend.org.uk/~sgtatham/bugs.html. We'd be grateful if you would then provide a more complete description of the problem.

We have instructions on debugging some types of problems at http://wiki.ubuntu.com/DebuggingProcedures.

At a minimum, we need:
1. The specific steps or actions you took that caused you to encounter the problem.
2. The behavior you expected.
3. The behavior you actually encountered (in as much detail as possible).
Thanks!

[Sebastien Bacher (seb128)]

The bug description doesn't even include the Ubuntu version used. Also you quote an apt command, how is that an update-notifier bug?

[Lorenzo (mad-dog)]

@Sebastien affect also me
Ubuntu 19.04

1. The specific steps or actions you took that caused you to encounter the problem.
add currently broken adoptopenjdk repository:
   wget -qO - https://adoptopenjdk.jfrog.io/adoptopenjdk/api/gpg/key/public | sudo apt-key add -
   sudo add-apt-repository --yes https://adoptopenjdk.jfrog.io/adoptopenjdk/deb/

2. The behavior you expected.
  I think notify for an update also if a source is broken

3. The behavior you actually encountered (in as much detail as possible).
  No update found, only error of broken source

[Sebastien Bacher (seb128)]

So the problem you are describing in the weird error in the notification icon?

[seahen (seahen123)]

Yes. My details are the same as Lorenzo's, except that I'm on Xubuntu 19.04.

[Launchpad Janitor (janitor)]

[Expired for update-notifier (Ubuntu) because there has been no activity for 60 days.]