Display a specific error message when corrupted image isn't rendered

As of now, when a user tries to upload a corrupted image to a Confluence page, a general error message would then be shown on the 'Insert files and images' popup.

Error retrieving attachments from Confluence. The server may be unavailable.

Given the user wasn't aware that the image is corrupted, they would then try to reupload the affected image for a number of times, which could then lead to OutOfMemory error mentioned in CONF-34076 that hangs the Insert files and images feature.

It would be better if Confluence can provide a more specific error message, so the user could have a clearer idea of what's causing the error without even have to look at the logs, as not every Confluence users will have access to the logs.

Insert files and images