fix: do not attempt to share image with empty list

Check for empty list and bail on sharing if no accounts found in
partition.
In cases where partition filtering removes all possible accounts from a
share list, attempting to share with an empty list will cause a
InvalidParameterCombination error to be raised.

Author: rthill91

awspub/image.py

@@ -189,6 +189,10 @@ def _share(self, share_conf: List[str], images: Dict[str, _ImageInfo]):
         """
         share_list = self._share_list_filtered(share_conf)
 
+        if not share_list:
+            logger.info("no valid accounts found for sharing in this partition, skipping")
+            return
+
         for region, image_info in images.items():
             ec2client: EC2Client = boto3.client("ec2", region_name=region)
             # modify image permissions