BUG/MINOR: spoe: Allow applet creation when closing the last one during stopping

BUG/MINOR: spoe: Allow applet creation when closing the last one during stopping

When the last SPOE applet is closed, for any reason, if there are still some
pending messages, in the shared sending queueu or the shared waiting queue, a
new applet is automatically created to be able to pocess these messages. Howver,
this was not performed when HAProxy was stopping. But it was an error because it
was then possible to abort some messages and reported them on error with the
status code set to 256.

So, now, it is still possible to create applet, if necessary, when HAProxy is
stopping.

This patch should partially fix the issue #2868. It must be backported to all
stable versions.