A block scalar whose last line is whitespace only and ends at end of
input without a break still owns one line break, which keep (+) chomping
preserves. libyaml records no break because there is no break byte, so
'- |+' over a spaces-only unterminated line yields '' instead of '\n'.
In scan_block_scalar_breaks, when the break loop stops at end of input
after consuming whitespace on that line, append one implicit '\n' to the
trailing breaks (used only by keep chomping). Content lines are
unaffected because they do not skip whitespace in this loop.
With this the ported engine emits the exact canonical event stream for
every valid case in the vendored YAML test suite: 308/308, ahead of
libyaml (252) and the old hand-rolled parser (267). Port score 307 -> 308.
Mihaela Mihaljevic
7898dcd1a9