Fix invalid listname and listsize not handled correctly in set_size

doc/lua_api.txt

@@ -1726,6 +1726,7 @@ methods:
 - is_empty(listname): return true if list is empty
 - get_size(listname): get size of a list
 - set_size(listname, size): set size of a list
+  ^ returns false on error (e.g. invalid listname or listsize)
 - get_width(listname): get width of a list
 - set_width(listname, width): set width of list; currently used for crafting
 - get_stack(listname, i): get a copy of stack index i in list

src/inventory.cpp

@@ -957,6 +957,9 @@ InventoryList * Inventory::addList(const std::string &name, u32 size)
 	}
 	else
 	{
+		//don't create list with invalid name
+		if (name.find(" ") != std::string::npos) return NULL;
+
 		InventoryList *list = new InventoryList(name, size, m_itemdef);
 		m_lists.push_back(list);
 		return list;

src/script/lua_api/l_inventory.cpp

@@ -117,24 +117,38 @@ int InvRef::l_set_size(lua_State *L)
 	NO_MAP_LOCK_REQUIRED;
 	InvRef *ref = checkobject(L, 1);
 	const char *listname = luaL_checkstring(L, 2);
+
 	int newsize = luaL_checknumber(L, 3);
+	if (newsize < 0) {
+		lua_pushboolean(L, false);
+		return 1;
+	}
+
 	Inventory *inv = getinv(L, ref);
 	if(inv == NULL){
-		return 0;
+		lua_pushboolean(L, false);
+		return 1;
 	}
 	if(newsize == 0){
 		inv->deleteList(listname);
 		reportInventoryChange(L, ref);
-		return 0;
+		lua_pushboolean(L, true);
+		return 1;
 	}
 	InventoryList *list = inv->getList(listname);
 	if(list){
 		list->setSize(newsize);
 	} else {
 		list = inv->addList(listname, newsize);
+		if (!list)
+		{
+			lua_pushboolean(L, false);
+			return 1;
+		}
 	}
 	reportInventoryChange(L, ref);
-	return 0;
+	lua_pushboolean(L, true);
+	return 1;
 }
 
 // set_width(self, listname, size)