fix: if CSV does not exists and it is read

[Miksus]

Now the CSV is created instead of raising an error.

This does not throw error if the CSV file does not exists:

from redbird.repos import CSVFileRepo

repo = CSVFileRepo(filename="myfile.csv", fieldnames=["name", "age", "color"])

repo.filter_by().all() # Previously gave an error

Instead, the file is created.