raise exception on invalid images (#999)

# What does this PR do?
This PR is meant to handle cases in which the images provided are
invalid.

## Who can review?

Anyone in the community is free to review the PR once the tests have
passed. Feel free to tag
members/contributors who may be interested in your PR.

@Narsil

---------
Co-authored-by: Nicolas Patry <patry.nicolas@protonmail.com>

server/text_generation_server/models/custom_modeling/idefics_image_processing.py

@@ -194,9 +194,14 @@ class IdeficsImageProcessor(BaseImageProcessor):
         if isinstance(image_url_or_urls, list):
             return [self.fetch_images(x) for x in image_url_or_urls]
         elif isinstance(image_url_or_urls, str):
-            response = requests.get(image_url_or_urls, stream=True, headers=headers)
+            response = requests.get(image_url_or_urls, stream=True, headers=headers, timeout=(1, 5))
             response.raise_for_status()
-            return Image.open(BytesIO(response.content))
+            try:
+                image = Image.open(BytesIO(response.content))
+                image.verify()
+            except Exception:
+                raise ValueError(f"Could not load image from url {image_url_or_urls}")    
+            return image
         else:
             raise ValueError(
                 f"only a single or a list of entries is supported but got type={type(image_url_or_urls)}"