private void addLiteralBoostsToFields(Schema schema) {
        Iterator i = matchingRankSettingsIterator(schema, RankProfile.RankSetting.Type.LITERALBOOST);
        while (i.hasNext()) {
            RankProfile.RankSetting setting = (RankProfile.RankSetting)i.next();
            SDField field = schema.getConcreteField(setting.getFieldName());
            if (field == null) continue;
            if (field.getLiteralBoost() < 0)
                field.setLiteralBoost(0);
        }
    }
Ensures there are field boosts for all literal boosts mentioned in rank profiles.
This is required because boost indices will only be generated by looking
at field boosts
config-model/src/main/java/com/yahoo/schema/processing/LiteralBoost.java