Function isCompilable

isCompilable(pattern?, flags?): boolean
Returns whether the given pattern can be compiled to a regex
Parameters
- Optionalpattern: null | string
  the pattern to check
- Optionalflags: string
  any combination of flag values
Returns boolean
whether the given pattern can be compiled to a regex
Example
```
isCompilable(undefined);    // false
isCompilable('foobar');    // true
isCompilable('[a-zA-Z0-9]+', 'g');    // true
```