Image file with variants issue for URL without file extension

[czim]

Storing an image file from an URL that has no file extension may result in an Imagine\Exception\InvalidArgumentException being thrown, with the message Saving image in "" format is not supported, please use one of the following extensions.

This occurs because imagine uses the file name to determine the type, instead of deriving the mime type. This may require altering czim/file-handling, or a config setting may be added to enforce file extensions based on mimetype, where omitted.