(message-sendmail-envelope-from): Obey `mail-envelope-from` even if set later

* lisp/gnus/message.el (message-sendmail-envelope-from): Change default.
(message--sendmail-envelope-from): New function.
(message-sendmail-envelope-from): Use it.
* lisp/mail/emacsbug.el (report-emacs-bug): Use it.
1 job for master in 56 minutes and 59 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
failed #4415
test-all

00:56:59

 
Name Stage Failure
failed
test-all Test
Makefile:319: recipe for target 'check-doit' failed
make[2]: Leaving directory '/builds/emacs/emacs/test'
make[2]: *** [check-doit] Error 1
make[1]: *** [check-expensive] Error 2
make: *** [check-expensive] Error 2
Makefile:294: recipe for target 'check-expensive' failed
make[1]: Leaving directory '/builds/emacs/emacs/test'
Makefile:959: recipe for target 'check-expensive' failed
ERROR: Job failed: exit code 1