Fix button animation resets

Mac/MainWindow/ArticleExtractorButton.swift

@@ -12,15 +12,19 @@ class ArticleExtractorButton: NSButton {
 	
 	var isError = false {
 		didSet {
+			if isError != oldValue {
 				needsDisplay = true
 			}
 		}
+	}
 	
 	var isInProgress = false {
 		didSet {
+			if isInProgress != oldValue {
 				needsDisplay = true
 			}
 		}
+	}
 	
 	override init(frame frameRect: NSRect) {
 		super.init(frame: frameRect)