Bug#870814: show message if unable to play video

[積丹尼 Dan Jacobson]

Package: libwebkit2gtk-4.0-37
Version: 2.17.5-2

$ set https://www.youtube.com/watch?v=3i1r12rkqAU
$ /usr/lib/i386-linux-gnu/webkit2gtk-4.0/MiniBrowser $@
User just sees a black box where the video is supposed to play.

Please instead show a message in there saying what the problem is. Don't
just show an empty black box.

-- System Information:
Debian Release: buster/sid
  APT prefers experimental
  APT policy: (990, 'experimental'), (500, 'unstable')
Architecture: i386 (i686)

Kernel: Linux 4.11.0-2-686-pae (SMP w/1 CPU core)
Locale: LANG=zh_TW.UTF-8, LC_CTYPE=zh_TW.UTF-8 (charmap=UTF-8), LANGUAGE=zh_TW.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash
Init: systemd (via /run/systemd/system)

Versions of packages libwebkit2gtk-4.0-37:i386 depends on:
ii  libatk1.0-0                             2.24.0-1
ii  libc6                                   2.24-14
ii  libcairo2                               1.14.10-1
ii  libegl1-mesa [libegl1-x11]              17.1.5-1
ii  libenchant1c2a                          1.6.0-11+b2
ii  libfontconfig1                          2.12.3-0.2
ii  libfreetype6                            2.8-0.2
ii  libgcc1                                 1:7.1.0-12
ii  libgcrypt20                             1.8.0-1
ii  libgdk-pixbuf2.0-0                      2.36.5-3
ii  libgl1-mesa-glx [libgl1]                17.1.5-1
ii  libglib2.0-0                            2.53.4-3
ii  libgstreamer-plugins-bad1.0-0           1.12.2-1
ii  libgstreamer-plugins-base1.0-0          1.12.2-1
ii  libgstreamer1.0-0                       1.12.2-1
ii  libgtk-3-0                              3.22.17-1
ii  libharfbuzz-icu0                        1.4.2-1
ii  libharfbuzz0b                           1.4.2-1
ii  libhyphen0                              2.8.8-5
ii  libicu57                                57.1-6
ii  libjavascriptcoregtk-4.0-18             2.17.5-2
ii  libjpeg62-turbo                         1:1.5.1-2
ii  libnotify4                              0.7.7-2
ii  libpango-1.0-0                          1.40.6-1
ii  libpng16-16                             1.6.31-1
ii  libsecret-1-0                           0.18.5-3.1
ii  libsoup2.4-1                            2.56.0-2
ii  libsqlite3-0                            3.19.3-3
ii  libstdc++6                              7.1.0-12
ii  libwayland-client0                      1.13.0-1
ii  libwayland-egl1-mesa [libwayland-egl1]  17.1.5-1
ii  libwayland-server0                      1.13.0-1
ii  libwebp6                                0.6.0-3
ii  libx11-6                                2:1.6.4-3
ii  libxcomposite1                          1:0.4.4-2
ii  libxdamage1                             1:1.1.4-2+b3
ii  libxml2                                 2.9.4+dfsg1-3
ii  libxslt1.1                              1.1.29-2.1
ii  zlib1g                                  1:1.2.8.dfsg-5

Versions of packages libwebkit2gtk-4.0-37:i386 recommends:
pn  gstreamer1.0-plugins-base  <none>
pn  gstreamer1.0-plugins-good  <none>

Versions of packages libwebkit2gtk-4.0-37:i386 suggests:
ii  libwebkit2gtk-4.0-37-gtk2  2.17.5-2

-- no debconf information