Item Generation question

[Epi]

After this, it selects the skill id. It will start at a certain value depending on the ilvl:

Above 36: 5
Between 24 and 36: 4
Between 18 and 24: 3
Between 18 and 11: 2
11 or lower: 1

This the becomes a base for all the skill ids. Then, it has a chance to be modified:

20% chance to add 1
50% chance to stay unmodified
20% chance to subtract 1
10% chance to subtract 2&nbsp; <- (typo fixed -Epi.)

If the item is low quality, then the skill id as of now is capped at 4.

Since the skill id is cannot be lower than 1 (otherwise skill from different class will be selected), I assume there's some verification for that, isn't it?

The question: what happens if, say, 1 is selected first, and then game rolls 10% chance to subtract 2 (making id = -1)? I believe, it's staying unmodified (i.e. +1), but knowing Blizzard it may be other way around.