attempting to tokenize lots of open parens results in a stack overflow #55
Description
https://gist.github.com/frewsxcv/3b427948da01685c95c26ab4a005c337
> cargo run
Compiling proc-macro2-foo v0.1.0 (file:///private/tmp/proc-macro2-foo)
Finished dev [unoptimized + debuginfo] target(s) in 2.4 secs
Running `target/debug/proc-macro2-foo`
thread 'main' has overflowed its stack
fatal runtime error: stack overflow
fish: 'cargo run' terminated by signal SIGABRT (Abort)
found via afl.rs