Merge branch 'develop_v1.2' of git.kdan.cc:Mac_PDF/PDF_Office into develop_v1.2

PDF Office/PDF Master/Class/PDFWindowController/Side/LeftSide/Search/KMSearchViewController.swift

@@ -319,6 +319,9 @@ extension KMSearchViewController {
     @IBAction func clearSearchHistoryAction(sender:Any) {
         UserDefaults.standard.removeObject(forKey: CPDFOfficeSearchHistoryKey)
         self.updateSearchMenu()
+        
+        //清空搜索词汇
+        self.previousSearchString = ""
     }
     
     @IBAction func escButtonAction(_ sender: Any) {