Fix error handling while deploying AppStream

Setting an error with second_error->message is going to work poorly
when second_error has never been set non-NULL.

Related to #1845, although not necessarily the full solution.

Signed-off-by: Simon McVittie <smcv@collabora.com>
Forwarded: https://github.com/flatpak/flatpak/pull/1867

Gbp-Pq: Name Fix-error-handling-while-deploying-AppStream.patch

flatpak (0.99.2-3) unstable; urgency=medium

  * Standards-Version: 4.1.5 (no changes required)
  * Put helper binaries in /usr/libexec as allowed by FHS 3.0
  * d/p/Fix-error-handling-while-deploying-AppStream.patch:
    Add a patch fixing error handling in system helper

[dgit import unpatched flatpak 0.99.2-3]

Import flatpak_0.99.2-3.debian.tar.xz

[dgit import tarball flatpak 0.99.2-3 flatpak_0.99.2-3.debian.tar.xz]

Import flatpak_0.99.2.orig.tar.xz

[dgit import orig flatpak_0.99.2.orig.tar.xz]