BUG: Add exception when different number of fields present in file lines
Addresses issue in #12519 by raising exception when 'filepath_or_buffer'
in 'read_csv' contains different number of fields in input lines.

However, according to tests the behaviour reported in bug is expected (lines 376-390): https://github.com/pydata/pandas/blob/master/pandas/io/tests/test_cparser.py#L376

So should those tests be removed?
