DNN-5852 Catch exception when uploaded image dimensions can't be determined

When uploading an ico file via the File Manager, it shows an error message, "Could not recognize image format. Parameter name: binaryReader" (though, it does, in fact, put the file on the disk).

This is because the `FileUploadController` is trying to get the dimensions of the image, but it doesn't know how to get the dimensions of that kind of file.