Merge remote-tracking branch 'remotes/kraxel/tags/fixes-20210810-pull-request' into staging

fixes for gtk, sdl and audio live migration.

# gpg: Signature made Tue 10 Aug 2021 13:18:30 BST
# gpg:                using RSA key A0328CFFB93A17A79901FE7D4CB6D8EED3E87138
# gpg: Good signature from "Gerd Hoffmann (work) <kraxel@redhat.com>" [full]
# gpg:                 aka "Gerd Hoffmann <gerd@kraxel.org>" [full]
# gpg:                 aka "Gerd Hoffmann (private) <kraxel@gmail.com>" [full]
# Primary key fingerprint: A032 8CFF B93A 17A7 9901  FE7D 4CB6 D8EE D3E8 7138

* remotes/kraxel/tags/fixes-20210810-pull-request:
  ui/sdl2: Check return value from g_setenv()
  audio: Never send migration section
  ui/gtk: retry sending VTE console input

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>