StopIteration thrown using load_csv
It looks like the CSV reader is expecting more lines in the file than there are. The CSV code is tested and should be working, so I doubt a bug as serious as "loading a CSV file is broken"... Guessing the issue is with the file. How many lines are needed at least for expecting CSV reader to work as expected?
Should I set `sample_size` greater than default 10? My CSV file is 15 lines long ....
Hi,

I try to load a csv file in sqlite db using `peewee 2.8.1`.
To do so, I've been using `playhouse.csv_utils`.
However, when I try to load CSV file, I've got a `StopIteration` thrown:
```
  File "/home/tuco/src/workspace/taxadb/lib/python3.5/site-packages/playhouse/csv_utils.py", line 309, in load_csv
    return loader.load()
  File "/home/tuco/src/workspace/taxadb/lib/python3.5/site-packages/playhouse/csv_utils.py", line 277, in load
    next(reader)
StopIteration
```

Below are the first 3 lines of my csv file:
```
ncbi_taxid,parent_taxid,tax_name,lineage_level
1,1,root,no rank
2,131567,Bacteria,superkingdom
...
```
and the way I call `load_csv`:
```python
...
load_csv(model, data, has_header=True, delimiter=",")
...
```

where `model` is as such:
```python
class Taxa(BaseModel):

    ncbi_taxid = pw.IntegerField(null=False, primary_key=True, unique=True)
    parent_taxid = pw.IntegerField(null=False)
    tax_name = pw.CharField()
    lineage_level = pw.CharField()
```
and `BaseModel` as below:
```python
db = peewee.Proxy()


class BaseModel(peewee.Model):
    class Meta:
        database = db
```
If I use a `database` object instead of a `model` another error is then thrown:
```python
...
  File "/home/tuco/src/workspace/taxadb/lib/python3.5/site-packages/playhouse/csv_utils.py", line 309, in load_csv
    return loader.load()
  File "/home/tuco/src/workspace/taxadb/lib/python3.5/site-packages/playhouse/csv_utils.py", line 266, in load
    self.analyze_csv()
  File "/home/tuco/src/workspace/taxadb/lib/python3.5/site-packages/playhouse/csv_utils.py", line 243, in analyze_csv
    **self.reader_kwargs)
  File "/home/tuco/src/workspace/taxadb/lib/python3.5/site-packages/playhouse/csv_utils.py", line 138, in extract_rows
    header, rows = rows[0], rows[1:]
IndexError: list index out of range
```

Is there something I do not use or set correctly?
Thx