Bugfix: Invalid comment handling in FSS Embedded Read.

Bugfix: Invalid comment handling in FSS Embedded Read.

The comments are not being properly processed because graph_first is not and should be being set to 0x1 at start.
As a result, the first comment is not being treated as a comment.

Make sure to reset the `graph_first` and `line_start` after processing the comment.
The comment starts at the line and so use `line_start` rather than `newline_last + 1`.
Remove dead code where `graph_first == 0x2` is being checked inside a block that requires `graph_first` to be `0x1`.

Update code comments about `graph_first` in several of the fl_fss read sources.

Add additional check for buffer string range when processing comments.

Update the runtime tests as appropriate.

I also noticed that several of these runtime tests use `--line` but are showing multiple lines.
I will address this bug in a separate commit.