Force econ item validation (#61)

For a long while, Valve blocked econ items from showing if they weren't
attached to a player that actually owned it.

An escape hatch was added in Gun Mettle to network the validation state of
items, since the owning player may have disconnected while one of their items
is held by another user.

Some VScript maps make use of this escape hatch for item visibility, so it's
probably fine to pull this in at this point.

scripting/cwx/item_entity.sp

@@ -22,6 +22,9 @@ stock int TF2_CreateItem(int defindex, const char[] itemClass) {
 
 		SetEntProp(weapon, Prop_Send, "m_iEntityQuality", 6);
 		SetEntProp(weapon, Prop_Send, "m_iEntityLevel", 1);
+
+		// if this is not toggled, then the weapon entity may not be visible
+		SetEntProp(weapon, Prop_Send, "m_bValidatedAttachedEntity", true);
 
 		DispatchSpawn(weapon);
 	}