Fix GETPART function implementation in base transform binding

[john-sanchez31]

The behavior of GETPART when there is nothing in the original string after the delimiter is currently inconsistent between the ansi/sqlite implementation versus what other dialects to akin to the Snowflake SPLIT_PART function (which GETPART is based on)

The current implementation of GETPART in the ansi/sqlite translation compared to GETPART in MySQL and Snowflake is as follow:

GETPART	ANSI/SQLITE	MySQL/SnowFlake
GETPART("string", "string", 1) ->	""	""
GETPART("string", "string", 2) ->	None	""
GETPART("string", "string", 3) ->	None	None
GETPART("hello.world.", ".", 1) ->	"hello"	"hello"
GETPART("hello.world.", ".", 2) ->	"world"	"world"
GETPART("hello.world.", ".", 3) ->	None	""
GETPART("hello.world.", ".", -1) ->	None	""
GETPART("hello.world.", ".", -2) ->	"world"	"world"
GETPART("hello.world.", ".", -3) ->	"hello"	"hello"
GETPART("abab", "ab", 1) ->	""	""
GETPART("abab", "ab", 2) ->	""	""
GETPART("abab", "ab", 3) ->	None	""
GETPART("abab", "ab", -1) ->	None	""
GETPART("abab", "ab", -2) ->	""	""
GETPART("abab", "ab", -3) ->	""	""

The desire behavior for the ansi/sqlite GETPART to maintain consistency through the dialects is the behavior of the MySQL/Snowflake implementation.