Do not target row group sizes if padding is set to 0

[asfimport]

The new padding commit will target row group sizes to the remaining space in a block if the space remaining is less than the padding size. This is the intended behavior if padding is set, but if padding is 0, then it will target a row group to be in any remaining bytes, even if that makes no sense.

The behavior when padding is 0 should be to always target row groups to the default row group size. This will match the existing behavior up to 1.8.0.

(In the error case, row groups will still span the block boundary, but will most likely be created with the minimum number of rows before checking whether or not it should be flushed.)

Reporter: Ryan Blue / @rdblue
Assignee: Ryan Blue / @rdblue

_{Note: This issue was originally created as PARQUET-325. Please see the migration documentation for further details.}

[asfimport]

Ryan Blue / @rdblue:
Merged #234. Thanks, Tianshuo!