Bug 20131: Inventory optional filters correct "For loan" addition

Bug 20131: Inventory optional filters correct "For loan" addition

In inventory, optional filters are build from authorize values categories used for items.notforloan, items.itemlost, items.withdrawn and items.damaged.

The bug is that description of value 0 is always "For loan".
This seems to be only for "notforloan".

Second bug is that if a description exists for "notforloan" value 0, it is not used.

This patch corrects by adding "For loan" only for "notforloan" authorized values and if there is no 0 value.
It changes the description added by code from "ignore" to a more unlikly user defined "__IGNORE__".

Test plan:
1) Make sure you have authorized values defined on items.notforloan, say "NFL" category, with at least a value and description but no 0 value
2) Make sure you have authorized values defined on items.itemlost, say "LOST" category, with 0 = "Not lost" and 1 = "Lost"
3) Go to inventory /cgi-bin/koha/tools/inventory.pl
4) Without patch you see "For loan" on both items.notforloan and items.itemlost
5) With patch you see "For loan" only in items.notforloan, you see for items.itemlost : "Not lost" and "Lost"
6) Create in authorized values category "NFL" a value 0 with description "Available"
7) Go to inventory /cgi-bin/koha/tools/inventory.pl
8) Without patch you see "For loan" in items.notforloan for value 0
9) With patch you see "Available" in items.notforloan for value 0

Signed-off-by: Séverine QUEUNE <severine.queune@bulac.fr>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>