from/to_base64 may return incorrect value when the value is null #4130
remove the duplicated base64 code
fix the base64 encoded string length is wrong， and this will cause the memory error
LSAN detected errors have been fixed by a prior pathch (#3326), but
there are still some ASAN detected errors.
This patch try to fix these errors to make Doris BE more robustness.
And then we can add CI run in LSAN/ASAN mode to detect memory errors
as early as possible.
