【fix】【内容编辑】文字块更换字体，属性面板和悬浮菜单未联动

PDF Office/PDF Master/Class/PDFTools/EditPDF/Window/KMEditPDFPopToolBarWindow.swift

@@ -117,7 +117,7 @@ import Cocoa
                                 model.fontName = self.model.fontNames.first
                             } else {
                                 model.isEnabled = false
-                                model.fontName = nil
+                                model.fontName = "Helvetica"
                             }
                         } else if key == .fontAdd {
                             model.isEnabled = self._fontSizeItemIsEnabled()