Bug#881605: qa.debian.org: popcon graphs are 0-byte files

[Simon McVittie <smcv@debian.org>]

Package: qa.debian.org
Severity: normal

QA pages like https://qa.debian.org/popcon.php?package=dbus contain a broken
image that does not display in browsers.

Downloading the image:

    wget -Otmp.png "https://qa.debian.org/cgi-bin/popcon-png?packages=dbus&show_installed=on&want_legend=on&want_ticks=on&date_fmt=%25Y-%25m&beenhere=1";

results in a 0 byte file, which is obviously not a valid PNG.

This prevents use of those graphs in determining whether a broken
package has a declining popcon score, which is useful input in
determining whether it should be removed from Debian.

Regards,
    smcv