Fix issue with header passed to read_csv

[galipremsagar]

We currently have an issue in read_csv where the following types of inputs fail:

In [1]: import dask.dataframe as dd

In [2]: !cat ../s.csv
x
x
x
A, B, C, D
1, 2, 3, 4
2, 3, 5, 1
4, 5, 2, 5


In [3]: dd.read_csv("../s.csv", header=3).compute()
---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
File /nvme/0/pgali/cudf/dask/dask/backends.py:136, in CreationDispatch.register_inplace.<locals>.decorator.<locals>.wrapper(*args, **kwargs)
    135 try:
--> 136     return func(*args, **kwargs)
    137 except Exception as e:

File /nvme/0/pgali/cudf/dask/dask/dataframe/io/csv.py:760, in make_reader.<locals>.read(urlpath, blocksize, lineterminator, compression, sample, sample_rows, enforce, assume_missing, storage_options, include_path_column, **kwargs)
    747 def read(
    748     urlpath,
    749     blocksize="default",
   (...)
    758     **kwargs,
    759 ):
--> 760     return read_pandas(
    761         reader,
    762         urlpath,
    763         blocksize=blocksize,
    764         lineterminator=lineterminator,
    765         compression=compression,
    766         sample=sample,
    767         sample_rows=sample_rows,
    768         enforce=enforce,
    769         assume_missing=assume_missing,
    770         storage_options=storage_options,
    771         include_path_column=include_path_column,
    772         **kwargs,
    773     )

File /nvme/0/pgali/cudf/dask/dask/dataframe/io/csv.py:620, in read_pandas(reader, urlpath, blocksize, lineterminator, compression, sample, sample_rows, enforce, assume_missing, storage_options, include_path_column, **kwargs)
    619     firstrow += header
--> 620 header = b"" if header is None else parts[firstrow] + b_lineterminator
    622 # Use sample to infer dtypes and check for presence of include_path_column

IndexError: list index out of range

The above exception was the direct cause of the following exception:

IndexError                                Traceback (most recent call last)
Cell In[3], line 1
----> 1 dd.read_csv("../s.csv", header=3).compute()

File /nvme/0/pgali/cudf/dask/dask/backends.py:138, in CreationDispatch.register_inplace.<locals>.decorator.<locals>.wrapper(*args, **kwargs)
    136     return func(*args, **kwargs)
    137 except Exception as e:
--> 138     raise type(e)(
    139         f"An error occurred while calling the {funcname(func)} "
    140         f"method registered to the {self.backend} backend.\n"
    141         f"Original Message: {e}"
    142     ) from e

IndexError: An error occurred while calling the read_csv method registered to the pandas backend.
Original Message: list index out of range

In [4]: import pandas as pd

In [5]: pd.read_csv("../s.csv", header=3)
Out[5]: 
   A   B   C   D
0  1   2   3   4
1  2   3   5   1
2  4   5   2   5

This PR fixes the issue by factoring in the header & firstrow parameters while making the parts split.

• Closes #xxxx
• Tests added / passed
• Passes pre-commit run --all-files

[phofl]

lgtm

[galipremsagar]

Bump for review/merge @jakirkham | @jrbourbeau

[jrbourbeau]

Thanks @galipremsagar -- this is in

[galipremsagar]

Thanks @jrbourbeau !