Unnecessary failing of GroupReduceCombineDriver

With a recent update (commit cbbcf7820885a8a9734ffeba637b0182a6637939) the GroupReduceCombineDriver was changed to not use an asynchronous partial sorter. Instead, the driver fills a sort buffer with records, sorts it, combines them, clears the buffer, and continues to fill it again.

The GroupReduceCombineDriver fails if a record cannot be serialized into an empty sort buffer, i.e., if the record is too large for the buffer.

Alternatively, we should emit a WARN message for the first record that is too large and just forward all records which do not fit into the empty sort buffer (maybe continue to count how many records were simply forwarded and give a second WARN message with this statistic).