Generating bounds from multi-column restrictions used to create
incorrect nonwrapping intervals, which only happened to work because
they're implemented as wrapping intervals underneath.
The following CQL restriction:
WHERE (a, b) >= (1, 0)
should translate to
(a, b) >= (1, 0), no upper bound,
while it incorrectly translates to
(a, b) >= (1, 0) AND (a, b) < empty-prefix.
Since empty prefix is smaller than any other clustering key,
this range was in fact not correct, since the assumption
was that starting bound was never greater than the ending bound.
While the bug does not trigger any errors in tests right now,
it starts to do so after the code is modified in order to
correctly handle empty intervals (intervals with end > start).
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