fixed return condition

[pvmm]

I tested this code and it seems that the condition is reversed.

[ped7g]

Review by reading the source:

yes, it should be ret nz and the dec hl should be done only when (hl) == 0 to return back to one leading zero char '0'.

[pvmm]

The ret nz guarantees that it is because it continues past that only if it is.