fix: dataset exists error in save Dataset modal (#21244)

* dataset exists error

* fixed flashing modal

superset-frontend/src/SqlLab/actions/sqlLab.js

@@ -1425,7 +1425,10 @@ export function createDatasource(vizOptions) {
 
         return Promise.resolve(json);
       })
-      .catch(() => {
+      .catch(error => {
+        getClientErrorObject(error).then(e => {
+          dispatch(addDangerToast(e.error));
+        });
         dispatch(
           createDatasourceFailed(
             t('An error occurred while creating the data source'),

superset-frontend/src/SqlLab/components/SaveDatasetModal/index.tsx

@@ -304,13 +304,12 @@ export const SaveDatasetModal: FunctionComponent<SaveDatasetModalProps> = ({
           [URL_PARAMS.formDataKey.name]: key,
         });
         createWindow(url);
+        setDatasetName(getDefaultDatasetName());
+        onHide();
       })
       .catch(() => {
         addDangerToast(t('An error occurred saving dataset'));
       });
-
-    setDatasetName(getDefaultDatasetName());
-    onHide();
   };
 
   const handleOverwriteDatasetOption = (value: SelectValue, option: any) => {