Fixed server segfault in getting unit veteran level info for middle-click request.
Fixed server segfault in getting unit veteran level info for
middle-click request.

adaxi/freeciv-web,tltneon/freeciv-web,adaxi/freeciv-web,sylvain121/freeciv-web-server,andreasrosdal/freeciv-web,sylvain121/freeciv-web-server,andreasrosdal/freeciv-web,tltneon/freeciv-web,tltneon/freeciv-web,tltneon/freeciv-web,adaxi/freeciv-web,sylvain121/freeciv-web-server,andreasrosdal/freeciv-web,andreasrosdal/freeciv-web,tltneon/freeciv-web,adaxi/freeciv-web,tltneon/freeciv-web,adaxi/freeciv-web,andreasrosdal/freeciv-web