Fix stack corruption in ui_read

Fix stack corruption in ui_read

This is an alternative to #20893

Additionally this fixes also a possible issue in UI_UTIL_read_pw:

When UI_new returns NULL, the result code would still be zero
as if UI_UTIL_read_pw succeeded, but the password buffer is left
uninitialized, with subsequent possible stack corruption or worse.

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/20957)