Sqllab dont send empty queries to db (#3459)

* add lanscape?

* prevent empty queries from being sent to db

* Revert "add lanscape?"

This reverts commit b3d6e80af4.

* improve code style

* nit

* unnit

* renit

superset/assets/javascripts/SqlLab/components/SqlEditor.jsx

@@ -76,6 +76,9 @@ class SqlEditor extends React.PureComponent {
     this.props.actions.queryEditorSetSql(this.props.queryEditor, sql);
   }
   runQuery(runAsync = false) {
+    if (!this.props.queryEditor.sql) {
+      return;
+    }
     let effectiveRunAsync = runAsync;
     if (!this.props.database.allow_run_sync) {
       effectiveRunAsync = true;