Allow invocation of annotation Processor's getCompletions even if process fails.

[lahodaj]

Writing code along these lines:

@ServiceProvider(service=|)
public class Test implements Runnable {
...
}

Code completion invoked at the place | does not contain options like Runnable. The reason is that the ServiceProviderProcessor.process will fail (due to the incomplete code), and then APTUtils.ErrorToleratingProcessor ignores even the getCompletions invocation.

The proposal is to split the valid flag in APTUtils.ErrorToleratingProcessor into two: one will be set if init fails, and this will block all the methods of the target processor, and one will be set when process fails, and that will only block the process method. As long as init passes, the getCompletions method may still be able to produce meaningful results, I think.

[dbalek]

Looks fine.