Fixed: SourceTitle if Book Title null in Discord ImportFailed event

Fixes READARR-FG

src/NzbDrone.Core/Notifications/Discord/Discord.cs

@@ -174,7 +174,7 @@ namespace NzbDrone.Core.Notifications.Discord
                 new Embed
                 {
                     Description = message.Message,
-                    Title = message.Book.Title,
+                    Title = message.Book?.Title ?? message.Message,
                     Text = message.Message,
                     Color = (int)DiscordColors.Warning
                 }

src/NzbDrone.Core/Notifications/NotificationService.cs

@@ -313,7 +313,7 @@ namespace NzbDrone.Core.Notifications
             // TODO: Build out this message so that we can pass on what failed and what was successful
             var downloadMessage = new BookDownloadMessage
             {
-                Message = GetBookIncompleteImportMessage(message.TrackedDownload.DownloadItem.Title),
+                Message = GetBookIncompleteImportMessage(message.TrackedDownload.DownloadItem.Title)
             };
 
             foreach (var notification in _notificationFactory.OnImportFailureEnabled())