When attempting to enter a sector with a land unit that can't go there
while the marching land units are all in the same sector, march stops
and prompts without removing the incapable land unit from the group.
If another land unit has already entered the sector, the group becomes
scattered.
This can happen when marching a mixed group of spies and non-spies
into a non-allied sector. Same for marching a mixed group of trains
and non-trains into a sector without rail, except such groups have
been disallowed since commit 36e41e5 (v4.3.7). Both screwed up when
spies and trains were added in 4.0.0
Remove the incapable land unit from the group when another land unit
can enter the sector. This avoids scattering land units.
Don't remove incapable land units when no land unit can enter the
sector. Without this, march would remove everyone and end then.
It can also happen when sectors or land units change while we're
sitting at the "Do you really want to abandon X,Y" prompt. I'm going
to fix that differently.
Signed-off-by: Markus Armbruster <armbru@pond.sub.org>
Markus Armbruster
c9fc05ae5b