ISBN Support (#1985)

* Fixed a bug where weblinks would always show

* Started to try and support ico -> png conversion by manually grabbing image data out, but it's hard as hell.

* Implemented ability to parse out ISBN codes for books and ISBN-13 codes for ComicInfo. I can't figure out ISBN-10.

* Fixed Favicon not working on anything but windows

* Implemented ISBN support into Kavita

* Don't round so much when transforming bytes

API/Controllers/ImageController.cs

@@ -173,6 +173,7 @@ public class ImageController : BaseApiController
     {
         var userId = await _unitOfWork.UserRepository.GetUserIdByApiKeyAsync(apiKey);
         if (userId == 0) return BadRequest();
+        if (string.IsNullOrEmpty(url)) return BadRequest("Url cannot be null");
 
         // Check if the domain exists
         var domainFilePath = _directoryService.FileSystem.Path.Join(_directoryService.FaviconDirectory, ImageService.GetWebLinkFormat(url));