Far from the origin a grid step smaller than the coordinate's
precision leaves x (or y) unchanged: at 1e16, 1e16 + 1 == 1e16. The
starting grid loop then never ended and allocated cells without limit,
even with the new maxCells budget (a hang dump reached 4.3 GB). Stop a
row or column once its step no longer advances.
Grids that advance are untouched, so the bit-identical differential
against the former sorted-list implementation still passes. Found by
the independent quality review of the Clipper2 overlap branch.
aj
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