Redstone comparators have two modes, comparison mode & subtraction mode.
Before this patch, the functions to turn comparators on or off attempted
to swap nodes with comparators in the same mode, but failed to determine
the correct replacement node, if the existing node was not a comparator.
When a comparator in an on state (e.g. powered by a filled cauldron) was
flooded, the flooding dropped the comparator and replaced the comparator
node that was to be swapped out with air, which lead to a server crash.
This patch changes the functions that turn comparators on or off so they
only swap existing nodes with comparators in the same mode if the name
of the replacement node can be determined – i.e. if it is not nil.
In commit 55009c257e that added vectors to
mcl_composters, mcl_hoppers was accidentally patched with a unrelated
change, updating it to get_item_group(). This mostly works, but in one
particular case the semantics of the return value differs. Instead of
returning 'nil' it returns '0'. That altered the evaluation of an if
condition, breaking the abm that sucks in items.
This commit fixes the conditional by explicitly comparing '~= 0'.
