Fix a potential NULL pointer deference in the LIKE optimization. The

Fix a potential NULL pointer deference in the LIKE optimization.  The
problem was introduced by the addition of generated columns
in check-in [b855acf1831943b3] (SQLite version 3.31.0, 2020-01-22).
Reported by Wang Ke in
[forum/forumpost/699b44b3ee|forum post 699b44b3ee].

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