Missing Error handling for delay below 0 when running lib from another Python file

[CaioRhoden]

Heyy, I've used this lib for a personal proejct and now I'm using it for a college course on Software Testing, applying some tests I identified the following problem in error handling

Issue description

When the delay argument (optional) is below the lib images without any warning or exception

Steps to reproduce the issue

1. Clone repository
**2. **cd google-images-download && sudo python setup.py install
3. In this respository create a python script
4. Import from google_images_download import google_images_download
5. Add the following commands

response = google_images_download.googleimagesdownload() 
arguments = {'keywords': 'dog', 'limit': 5, 'delay': -0.1}
response.download(arguments)

6. Run script

What's the expected result?

• Some error message to explicit that is not possible to download images with negative delay interval

What's the actual result?

• It downloads the expected number of images

Additional details / screenshot