sqlite: skip return() on exhausted virtual table iterators

[trivikr]

Fixes: #66518

Once a virtual table iterator's next() reports done: true, the iterator is finished, so return() must not be called. This matches for...of, which calls return() only on abrupt termination. Before this change, an empty custom iterable with a throwing return() made an otherwise successful query fail.

CloseIterator() now skips cursors whose iteration has completed. That covers both xClose and cursor re-filtering. Early termination (LIMIT, break, re-filter mid-scan) still calls return().

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Assisted-by: claude:opus-5.5

[nodejs-github-bot]

Review requested:

• @nodejs/sqlite

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.40%. Comparing base (bbd566d) to head (5925401).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #66519      +/-   ##
==========================================
- Coverage   92.74%   90.40%   -2.35%     
==========================================
  Files         422      791     +369     
  Lines      193170   275991   +82821     
  Branches    29783    52980   +23197     
==========================================
+ Hits       179160   249505   +70345     
- Misses      13682    16902    +3220     
- Partials      328     9584    +9256     

Files with missing lines	Coverage Δ
src/node_sqlite.cc	81.94% <100.00%> (ø)

... and 498 files with indirect coverage changes

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