fixed #216 disabled save button for empty filters

Author: shubhendusaurabh

src/shared/components/challenge-listing/Filters/FiltersPanel/index.jsx

@@ -136,6 +136,7 @@ export default function FiltersPanel({
         <button
           styleName="blue"
           className="tc-blue-btn"
+          disabled={_.isEmpty(filterState)}
           onClick={onSaveFilter}
         >Save filter</button>
       </div>