app_queue: Fix crash when unloading module.

app_queue: Fix crash when unloading module.

When unloading the app_queue module the members in each queue are
destroyed and as part of this they are removed from the pending
members container. Unfortunately a crash would occur as the container
was destroyed before the members were removed.

This change tweaks ordering so the container destruction occurs
after the members are destroyed.

ASTERISK-16115

Change-Id: I48c728668c55aee3d05b751a5d450fb57e87f44b