Death of an advanced unit

[Lincoln Peters]

Recently, I sent a bug report that stated that in Xconq 7.4.1, I found
that it segfaulted whenever an advanced unit was destroyed by something
other than starvation.  I later reported that the problems stopped when
I tried the CVS sources (7.5pre).  I have some new information now.

It seems that the segfault occurs if an advanced unit is destroyed by
something other than starvation (combat, hp-to-garrison, etc.), but not
if the unit is under construction.  I think that Hans Ronne noted that
the segfaults were most likely tied to terrain usage, which would
explain why it doesn't segfault if the advanced units is incomplete (at
that point, it's not using the terrain for anything).