nsc: Reject array selectors in conditions

nsc: Reject array selectors in conditions

Array selectors were introduced for xdump (commit 612f2da, v4.2.18).
Since there is no syntax for subscripting arrays in conditions and
survey, we silently assume index zero.  Unclean.  Reject the selector
instead.

Affects ship selectors cargostart, cargoend, amtstart, amtend (since
commit 32011f1, v4.2.19), nat selectors relations (commit 0a44c48,
v4.3.0), contacts (commit c345ab8, v4.3.0), rejects (commit 6844c94,
v4.3.4).  The other array selectors aren't visible in conditions.  No
array selectors are visible in survey.

Signed-off-by: Markus Armbruster <armbru@pond.sub.org>