Supply: Inventory Level special codes

In-stock quantity usually returns a non-negative number.

However, sometimes negative numbers representing special codes are returned.

Here is the definition for these special codes:

-1: "Non-Stocked"

-2: "Yes" (generic, unspecified quantity but is in stock)

-3: "Unknown" (no quantity value is provided, or the value was not an integer)

-4: "RFQ"