[BUG] APPLY substr function not using -1 count as documented - [MOD-6959]

[joeywhelan]

Per the documentation, a -1 count in the substr function is supposed to return the rest of the string from the offset.

Return the substring of s, starting at offset and having count characters.
If offset is negative, it represents the distance from the end of the string.
If count is -1, it means "the rest of the string starting at offset".

That's not what is happening. See example below. Redis Search version = 2.8.12

> FT.CREATE idx SCHEMA date TEXT SORTABLE
"OK"

> HSET key date "04-03-2024"
(integer) 1

> FT.AGGREGATE idx * APPLY 'substr(@date,6,-1)' AS Year
1) "1"
2) 1) "date"
   2) "04-03-2024"
   3) "Year"
   4) "202"