open-api: javadoc parser NPE

[kliushnichenko]

The following example leads to a build failure

@Path("/")
public class HelloController {

    @GET
    public Mono<String> hello() {
        return Mono.fromCallable(() -> "hello")
                .onErrorContinue((e, o) -> e.printStackTrace());      // <- root cause line
    }
}

Stacktrace:

Caused by: java.lang.NullPointerException
    at io.jooby.internal.openapi.javadoc.JavaDocStream$ASTNode$1.getNextSibling (JavaDocStream.java:238)
    at io.jooby.internal.openapi.javadoc.JavaDocStream$3.next (JavaDocStream.java:171)
    at java.util.Iterator.forEachRemaining (Iterator.java:133)

v4.0.13