core grammar: `tree-sitter playground` webpage fails

[gjsjohnmurray]

From DevTools on the browser page:

Aborted() tree-sitter.js:2285:10
    abort http://127.0.0.1:8000/tree-sitter.js:2285
    __abort_js http://127.0.0.1:8000/tree-sitter.js:3218
    abort http://127.0.0.1:8000/tree-sitter.wasm:165524
    ts_malloc_default http://127.0.0.1:8000/tree-sitter.wasm:5731
    stack__iter http://127.0.0.1:8000/tree-sitter.wasm:33542
    ts_parser__recover http://127.0.0.1:8000/tree-sitter.wasm:42110
    ts_parser__recover http://127.0.0.1:8000/tree-sitter.wasm:41536
    ts_parser_parse_wasm http://127.0.0.1:8000/tree-sitter.wasm:123478
    parse http://127.0.0.1:8000/tree-sitter.js:3878
    handleCodeChange http://127.0.0.1:8000/playground.js:220
    handleLanguageChange http://127.0.0.1:8000/playground.js:206

Uncaught (in promise) RuntimeError: Aborted(). Build with -sASSERTIONS for more info.
    abort http://127.0.0.1:8000/tree-sitter.js:2288
    __abort_js http://127.0.0.1:8000/tree-sitter.js:3218
    parse http://127.0.0.1:8000/tree-sitter.js:3878
    handleCodeChange http://127.0.0.1:8000/playground.js:220
    handleLanguageChange http://127.0.0.1:8000/playground.js:206
tree-sitter.js:2288:15

[davem-intersys]

This is likely related to the zero-length token in #8, and it ends up running out of memory.