Fix a off-by-one error in code generation that comes up when

Fix a off-by-one error in code generation that comes up when
doing a DISTINCT query against a virtual table with an OR term in the
WHERE clause and where the ORDER BY clause has 64 or more references to
the result set.  [forum:/forumpost/dfe8084751|Forum post dfe8084751].
The error is harmless in production builds, but might cause an assertion
fault in a debugging build.

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