Bug#876981: apt-get download ignores invalid Architecture

[Sebastian Hahn <debian_bugs@sebastianhahn.net>]

Package: apt
Version: 1.4.7
Severity: normal

Dear Maintainer,

specifying an invalid architecture for apt-get download does not give an error
message. Instead return value is 0 and the i386 version of the package is
downloaded:

$ apt-get download -o APT::Architecture=omgwtfbbq xz-utils
Get:1 http://ftp.de.debian.org/debian stretch/main i386 xz-utils i386
5.2.2-1.2+b1 [271 kB]

Similarly, apt-get install doesn't just give a short explanation about the
wrong architecture but spits out pages of missing dependencies.

Cheers
Sebastian

-- System Information:
Debian Release: 9.1
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386, arm64

Kernel: Linux 4.9.0-3-amd64 (SMP w/8 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=en_US:en (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages apt depends on:
ii  adduser                 3.115
ii  debian-archive-keyring  2017.5
ii  gpgv                    2.1.18-6
ii  init-system-helpers     1.48
ii  libapt-pkg5.0           1.4.7
ii  libc6                   2.24-11+deb9u1
ii  libgcc1                 1:6.3.0-18
ii  libstdc++6              6.3.0-18

Versions of packages apt recommends:
ii  gnupg   2.1.18-6
ii  gnupg2  2.1.18-6

Versions of packages apt suggests:
pn  apt-doc         <none>
ii  aptitude        0.8.7-1
ii  dpkg-dev        1.18.24
pn  powermgmt-base  <none>
ii  python-apt      1.4.0~beta3