click.prompt combined with click.Path skips path validation for prompt default

[JWCook]

If using click.prompt with both click.Path and a default value, any user input will be validated through click.Path, but the default value will not be.

Example:

>>> import click
>>> click.prompt('Path', type=click.Path(exists=True), default='/invalid/path')
# Invalid user input raises error
Path [/invalid/path]: /some/other/invalid/path
Error: Path "/some/other/invalid/path" does not exist.
# Invalid default value does not raise error
Path [/invalid/path]:
'/invalid/path'

Tested with click 6.7, and python 2.7.13 and 3.6.1.

[d-ganchar]

link to PR