[CS2] Fix #4575: Leading asterisk

[GeoffreyBooth]

Fixes #4575. Before:

coffee -bpe '*'
TypeError: Cannot read property '0' of undefined
    at Lexer.literalToken (./coffeescript/lib/coffeescript/lexer.js:889:39)

After:

./bin/coffee -bpe '*'
[stdin]:1:1: error: unexpected *
*
^

[GeoffreyBooth]

These one-character PRs are part of my master plan to rise in the “most commits” rankings.

[jashkenas]

You're climbing fast!