[fix] Handle zero-width horizontal crops

[AryanRG]

Summary

• handle degenerate zero-width quadrilaterals in horizontal crop extraction without raising IndexError;
• return the existing empty-crop placeholder so the predictor's current filtering keeps crops, boxes, and objectness scores aligned;
• cover direct geometry behavior plus mixed and all-collapsed OCR/KIE predictor paths.

The oriented crop path is unchanged. Boxes with NaN x coordinates also produce an empty crop instead of the previous IndexError; broader non-finite polygon validation is outside this patch.

Validation

• regression before fix: 12 expected IndexErrors, with 8 oriented controls passing;
• revised regression and OCR/KIE integration nodes: 20 passed;
• complete geometry module: 56 passed;
• focused predictor selection: 7 passed;
• builders: 40 passed;
• adjacent detection/recognition utilities: 74 passed;
• dataset crop caller: 2 passed;
• existing OCR/KIE predictor nodes: 10 passed;
• pre-commit, Ruff check/format, git diff --check, and mypy doctr/ passed.

The broader local make test run stopped after 159 passes because WeasyPrint could not load the host's missing libgobject-2.0-0 native library. A standalone WeasyPrint import fails identically, so full-suite and coverage equivalence are not claimed.