Verifies Sources don’t contain duplicate bundle IDs

AltStore assumes all apps have unique bundle IDs per source. Weird bugs can occur when this is not the case (such as merging multiple store listings into one), so we now verify upfront whether source contains duplicate bundle IDs before saving.

AltStore/Managing Apps/AppManager.swift

@@ -415,10 +415,13 @@ extension AppManager
                     switch result
                     {
                     case .success(let source): fetchedSources.insert(source)
-                    case .failure(let error):
+                    case .failure(let nsError as NSError):
                         let source = managedObjectContext.object(with: source.objectID) as! Source
-                        source.error = (error as NSError).sanitizedForSerialization()
+                        let title = String(format: NSLocalizedString("Unable to Refresh “%@” Source", comment: ""), source.name)
+                        
+                        let error = nsError.withLocalizedTitle(title)
                         errors[source] = error
+                        source.error = error.sanitizedForSerialization()
                     }
                     
                     dispatchGroup.leave()