Always shatter glass items within bins thrown by a catapult.

The glass materials have impact strength copied from compression
strength, so the items had 1/5 chance to survive without damage.
Since glass is infinite, it makes sense to make it single-use.

plugins/siege-engine.cpp

@@ -275,7 +275,7 @@ static bool apply_impact_damage(df::item *item, int minv, int maxv)
 
     // Instant fracture?
     int fracture = strength.fracture[type];
-    if (fracture <= power)
+    if (fracture <= power || info.material->flags.is_set(material_flags::IS_GLASS))
     {
         item->setWear(3);
         return false;