when the webview evaluete javascript fail will cause crash

[zhipcui]

• (void)WKFlushMessageQueue {
  [_webView evaluateJavaScript:[_base webViewJavascriptFetchQueyCommand] completionHandler:^(NSString* result, NSError* error) {
  [_base flushMessageQueue:result];
  }];
  }

The reason:
if the result == nil, then flushMessageQueue try to _deserializeMessageJSON a nill object.

[marcuswestin]

Fixed in v5.0.2