This should be a simpler solution.

select N2.n as dan, N.n - 1 as Ura, isnull(sum(SaleQTY), 0) as D

from dbo.GetNums(24) as N cross join dbo.GetNums(31) as N2

left join (select datepart(day, SaleTime) as Dan, datepart(hh, SaleTime) as Ura, sum(SaleQTY) as SaleQTY

from dbo.#SalesTestData

group by datepart(day, SaleTime), datepart(hour, SaleTime))as D on D.Dan = N2.n and D.Ura = (N.n - 1)

group by N2.n, N.n

order by 1, 2

Uncle Goole will tell you more about function GetNums ( = Virtual Auxiliary Table of Numbers).