is_damageable was always true

<Someone> noticed that is_damageable used the address of is_rottable
instead of calling it.  Unfortunately, there doesn't seem to be a good
compiler warning to detect uses of function addresses as booleans.

doc/fixes34.2

@@ -35,6 +35,7 @@ dropping from height or throwing a normal container may damage contents
 some Magicbane messages treated "erinys" as plural
 initialize artifacts before processing $WIZKIT
 clean up inconsistency between various places quaff is documented
+is_damageable was using is_rottable incorrectly
 
 
 Platform- and/or Interface-Specific Fixes

include/objclass.h

@@ -75,7 +75,7 @@ struct objclass {
 #define is_corrodeable(otmp)	(objects[otmp->otyp].oc_material == COPPER || objects[otmp->otyp].oc_material == IRON)
 
 #define is_damageable(otmp) (is_rustprone(otmp) || is_flammable(otmp) || \
-				is_rottable || is_corrodeable(otmp))
+				is_rottable(otmp) || is_corrodeable(otmp))
 
 	schar	oc_subtyp;
 #define oc_skill	oc_subtyp   /* Skills of weapons, spellbooks, tools, gems */