Once the class name is found, stop looking for it.

It is possible for two `class` tokens to be in the 512 byte block that is searched.  This would happen if a test case is checking for class names.

This came up for me when I was making a type-safe strict mode IOCContainer.  I wanted to make sure the name of the class instantiated is as expected, and I used `ClassName::class` to get the name of the expected class as a string.  The parser interprets this as a `class` token.

The symptom was the loader was attempting to load a class with the correct namespace, but the class name was an empty string.
Hack does not support multiple levels of break.  The type checker gives me

```
Yeah...we're not going to support continue/break N. It makes static analysis tricky and it's not really essential (Parsing[1002])
```