Created attachment 170098 [details] [review]
Fix.

Sometimes when you switch from the screen with vte window to a different screen the application should continue its output stream to the (non-visible) window.
Sometimes it does not and the applications keeps stopped.

Reproducer:
gnome-terminal --disable-factory -e /tmp/termlock &>/tmp/out

/tmp/termlock is:
#! /bin/sh
i=0;while :;do echo \
---------------------------------------------$i;i=$[$i+1];done

Always switch away from the screen with this window and run:
strace -p <pid of termlock>

to see if it still writes there.  Sometimes its write() syscall hangs.

Debug (/tmp/out) tail in this hanging case (using VTE_DEBUG=all):
[...]
-].read 8176/4096 bytes, again? no, active? yes
removed poll of vte_terminal_io_read
Visibility (unobscured -> fully-obscured).
change visibility: unobscured -> fully-obscured.
Removing terminal from active list
Removing update timeout


The fix has been tested and makes sense only together with the other fix, going
to link the two Bugs together.