Android Webview custom error message

Hello everyone, I added a custom error message from Webview to my app, however the default Android message still appears for a few seconds, how do I resolve it?

Here is the code:

webview.setWebViewClient(new WebViewClient() {
                public void onReceivedError(WebView webView, int errorCode, String description, String failingUrl) {
                    try {
                        webview.stopLoading();
                    } catch (Exception e) {
                    }

                    if (webView.canGoBack()) {
                        webView.goBack();
                    }
                    webview.stopLoading();
                    webview.loadUrl("about:blank");
                    AlertDialog alertDialog = new AlertDialog.Builder(Textures.this).create();
                    alertDialog.setTitle("Sem conexão");
                    alertDialog.setMessage("Para ver as texturas é preciso conexão com Internet!");
                    alertDialog.setButton(DialogInterface.BUTTON_NEGATIVE, "Ok", new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog, int which) {
                                finish();
                            }
                        });

                    alertDialog.show();
                    super.onReceivedError(webView, errorCode, description, failingUrl);
                }
            });

Whenever there is no internet the message appears, however as previously said the default message of Android appears a few seconds before.