In the following SQL, the virtual machine references an uninitialized
register.  This is harmless, but it still needs to be fixed.

<blockquote><verbatim>
CREATE TABLE t1(b, c, PRIMARY KEY(b,c)) WITHOUT ROWID;
CREATE UNIQUE INDEX t1b ON t1(b);
UPDATE t1 SET b=1 WHERE b='';
</verbatim></blockquote>

This problem has existed in the code since support for WITHOUT ROWID
tables was added with SQLite 3.8.2 (2013-12-06).  The problem was
discovered by OSSFuzz.