Decorrelator gives empty result after decorrelating sort rel with null offset and fetch

It seems like I introduced a bug with the recent decorrelator patch. Sort rel with null offset and fetch would end up becoming an empty value since decorrelator would call sortLimit builder with 0 limit and 0 offset. It should pass negative values to builder when values are null.

https://github.com/apache/calcite/blob/e863294ccfbed9dd520c999f75ed0bbe03f9fb1d/core/src/main/java/org/apache/calcite/sql2rel/RelDecorrelator.java#L423