[C++] Table::CombineChunks() returns incorrect results if Table has no column

>>> pa.table([[1]], ["a"])
pyarrow.Table
a: int64
>>> t = pa.table([[1]], ["a"])
>>> t.num_rows
1
>>> t1 = t.drop(["a"])
>>> t1.num_rows
1
>>> t2 = t1.combine_chunks()
>>> t2.num_rows
0