ENH: cast unrecognised value as na in read_csv
#### Is your feature request related to a problem?

I have a csv file which can contain some mission part due to IO problem.

Say if I have a csv file

```
0 -1 -10
1 -2 -20
2 -3 -30
```
However, due to the buffer problem, it can become

```
0 -1 -10
1 -2 -20
2 -3 -
```

If I use pandas.read_csv to read it, I will get:

```
  File "/Users/XXX/opt/miniconda3/envs/mda_dev/lib/python3.7/site-packages/pandas/io/parsers.py", line 610, in read_csv
    return _read(filepath_or_buffer, kwds)
  File "/Users/XXX/opt/miniconda3/envs/mda_dev/lib/python3.7/site-packages/pandas/io/parsers.py", line 468, in _read
    return parser.read(nrows)
  File "/Users/XXX/opt/miniconda3/envs/mda_dev/lib/python3.7/site-packages/pandas/io/parsers.py", line 1057, in read
    index, columns, col_dict = self._engine.read(nrows)
  File "/Users/XXX/opt/miniconda3/envs/mda_dev/lib/python3.7/site-packages/pandas/io/parsers.py", line 2061, in read
    data = self._reader.read(nrows)
  File "pandas/_libs/parsers.pyx", line 756, in pandas._libs.parsers.TextReader.read
  File "pandas/_libs/parsers.pyx", line 771, in pandas._libs.parsers.TextReader._read_low_memory
  File "pandas/_libs/parsers.pyx", line 850, in pandas._libs.parsers.TextReader._read_rows
  File "pandas/_libs/parsers.pyx", line 982, in pandas._libs.parsers.TextReader._convert_column_data
  File "pandas/_libs/parsers.pyx", line 1056, in pandas._libs.parsers.TextReader._convert_tokens
ValueError: could not convert string to float: '-'
```

#### Describe the solution you'd like

I wonder if it is possible to cast any unrecognised value as NA rather than raise a Value error

#### API breaking implications

N/A

#### Describe alternatives you've considered

perhaps just skip this line?
