Any projects which want to use Hush code from now on will need to be licensed as
GPLv3 or we will send the lawyers: https://www.softwarefreedom.org/
Notably, Komodo (KMD) is licensed as GPLv2 and is no longer compatible to receive
code changes, without causing legal issues. MIT projects, such as Zcash, also cannot pull
in changes from the Hush Full Node without permission from The Hush Developers,
which may in some circumstances grant an MIT license on a case-by-case basis.
Previously, an input with invalid characters would result in out-of-bounds
reads, potentially exposing up to 224 bytes of memory following the location of
the CHARSET constant. This commit fixes the function to return an empty string,
which is what was originally documented as happening.
