Trailing comments in query causes "string index out of range"

I'm using graphiQL for testing my API where it is fairly common practice to comment out a query and write a new one.

```
{info}
```

Will run fine.

```
{info}
#
```

Will fail with "string index out of range" on line 268 of lexer.py (char=body[position])

I could be wrong - but shouldn't that be a >= rather than >?