Get the error index of an SVTA error code, per the spec's
code mod 1000 rule. The index identifies the specific error within
its category: native indices are 0-99, embedded external codes (HTTP,
VAST) are 100-999.
Parameters
code: number
An SVTA error code.
Returns number|undefined
The error index within the code's category, or undefined
if the code is not a non-negative integer.
Get the error index of an SVTA error code, per the spec's
code mod 1000rule. The index identifies the specific error within its category: native indices are 0-99, embedded external codes (HTTP, VAST) are 100-999.