[sql_lab]Disabled run query button if sql query editor is empty (#4728)

* Disabled run query button if sql query editor is empty

* Removing unnecessary white space

* Fix failing test for sql props

* Adding sql variable into propTypes and defaultProps

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

@@ -215,6 +215,7 @@ class SqlEditor extends React.PureComponent {
                 runQuery={this.runQuery}
                 selectedText={qe.selectedText}
                 stopQuery={this.stopQuery}
+                sql={this.state.sql}
               />
             </span>
             <span className="m-r-5">