Used cached row

src/terminal/widget.ts

@@ -171,7 +171,7 @@ class TerminalWidget extends Widget {
       return Promise.reject(void 0);
     }
     return this._session.reconnect().then(() => {
-      let rows = this._term.getOption('rows');
+      let rows = this._sessionSize[0];
       this._term.refresh(0, rows - 1);
     });
   }