reindexItems replaced the FIRST [n] index in a data-path, which for nested
arrays (e.g. services[1].specs.items) rewrote the OUTER array index instead
of the item's own index. Deleting or adding an item scattered paths across
services[0..n], produced sparse arrays (null items) and schema errors like
'$.details.services[1].specs.items[0]: string érték szükséges'.
Rewrite only the index directly following the reindexed array's path prefix;
drop the now-redundant str-item special case.
Closes MITHOME-30
Do Siki