fix SkSL lexer's handling of invalid characters

Bug: skia:8831
Change-Id: I3198c86af971c3340ccf7cc1d7dede6dd48939fb
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/204980
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Kevin Lubick <kjlubick@google.com>
Auto-Submit: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
3 files changed