more weapon shattering

The Kop Kaptain's rubber hose shatters from the force of your blow!
Rubber hoses are an individual exception that would need to be dealt
with explicitly, since the PLASTIC they're made of is floppy rather
than rigid as for other PLASTIC items.

src/uhitm.c

@@ -575,7 +575,7 @@ int thrown;
 			  ((wtype = uwep_skill_type()) != P_NONE &&
 			    P_SKILL(wtype) >= P_SKILLED) &&
 			  ((monwep = MON_WEP(mon)) != 0 &&
-			   objects[monwep->otyp].oc_material >= WOOD &&
+			   !is_flimsy(monwep) &&
 			   !obj_resists(monwep,
 				 50 + 15 * greatest_erosion(obj), 100))) {
 			/*