[formatter] IndexOutOfBoundsException in applying formatter to code having errors

Relates to:
https://bugs.eclipse.org/bugs/show_bug.cgi?id=471825
https://github.com/vi-eclipse/Eclipse-JDT/issues/10

### How to reproduce the bug:

The code given in this comment: https://bugs.eclipse.org/bugs/show_bug.cgi?id=471825#c11

or

```
package testproject;

public class Application extends B {
protected int f = 11;
```

###

As far I can understand, it fails because we ignore errors if the kind is K_COMPILATION_UNIT: https://github.com/eclipse-jdt/eclipse.jdt.core/blob/master/org.eclipse.jdt.core/formatter/org/eclipse/jdt/internal/formatter/DefaultCodeFormatter.java#L317
and it proceeds to find the closing bracket.

For me, if a code has errors then we should not format it at all but I can't find any comment on why `ignoreErrors ` was set to true for K_COMPILATION_UNIT in the original code which was introduced in this commit: https://github.com/eclipse-jdt/eclipse.jdt.core/commit/b0e753009ffb9bf0d92f75f621fb0d6188adb57e

One possible fix could be to not ignore errors: https://github.com/eclipse-jdt/eclipse.jdt.core/pull/1434

But it fails tests and before fixing those tests I would like to confirm this is the expected behavior.