知识库引用，事件分类不必填引起的BUG

src/views/processing.vue

@@ -907,7 +907,7 @@ export default {
         }
       });
       this.selected = selected;
-      this.selectedCategoryTxt=selected[selected.length - 1];
+      this.selectedCategoryTxt=selected.length?selected[selected.length - 1]:'';
       this.model.category=selectedVal;
       localStorage.setItem("category", JSON.stringify(selectedIndex));
       localStorage.setItem("categoryVal", JSON.stringify(selectedVal));