Progress: Handle basic list combining/joiner at start and fix unit test.

Progress: Handle basic list combining/joiner at start and fix unit test.

For lists, if the start of a line is a combining/joiner, then it must be treated as Content even if it would otherwise be a valid Object on that line.

The unit test actually has to handle when `F_okay_eos` or `F_okay_stop` is returned on content read.
The basic list doesn't know if the content is a valid object or not.
It can be assumed, but the function does not do this.

The caller must handle incrementing found.used when either `F_okay_eos` or `F_okay_stop` is returned.
Update the comment on this as well.

Properly verify that `newline_last` is in fact a new line by checking it against the `begin` position.
The basic list already has `begin`, but extended list has `begin` added to perform this check.