[Freeciv-Dev] (PR#13342) pubserver 2.0 crash in found_new_tech

["Jason Short" <jdorje@xxxxxxxxxxxxxxxxxxxxx>]

<URL: http://bugs.freeciv.org/Ticket/Display.html?id=13342 >

Argh!

This crash is caused by the patch that fixes bug #13198.

In last crash (442921), techpenalty is set to 0.  When a unit
investigates a hut, it doesn't (as one might expect) pick a tech and
give it to you.  Instead it picks a tech, sets your research to be on
that tech, completes research, then restores the previous research. 
However now picking a random tech uses choose_tech() which may complete
the tech immediately if there are enough bulbs, which may sometimes
happen if techpenalty is less than 100.  Thus the tech completes, and if
there's no goal then the research target is set back to A_UNSET which is
what is passed in to found_new_tech.

For S2_0 the solution is to revert the 13198 patch.  Maybe one of the
other patches to fix this bug can be used and will be less invasive.

For the development branch the fix is harder, since we probably want to
fix 13198 as well.  I suggest changing pick_random_tech so that it
doesn't have any side effects just returns the tech.  Then the caller
will have to call found_new_tech or choose_tech as needed to make use of
the random tech that is returned.

-jason