A block scalar terminated by a less-indented comment line failed with a
spurious 'unexpected indentation': once the smaller indentation ended the
scalar, the comment's own column was processed as a dedent, and because no
indentation level held that width the dedent raised an error. A comment's
indentation does not participate in block structure, so a comment that ends
a block scalar is now left for the main loop to scan, with the block
scalar's own first content line (which may itself begin with '#') still
treated as content.
Separately, a whitespace-only line indented past a block scalar's content
level lost its surplus spaces because the width was consumed before the
line was recognized as blank; the surplus is now preserved as the line's
content, so an over-indented blank contributes the correct value.
Measured against the official YAML test-suite, parse-level conformance
rises from 240/333 (72.1%) to 243/333 (73.0%) with matching value-level
gains, and no regression.
