Fix launching empty query

If the query is prefixed with a space the launched entry should not be
added to the history, in case there is nothing after the query the trimmed string would be empty.

lib/runnerresultsmodel.cpp

@@ -191,7 +191,7 @@ void RunnerResultsModel::setQueryString(const QString &queryString)
     m_hasMatches = false;
     if (queryString.isEmpty()) {
         clear();
-    } else {
+    } else if (!queryString.trimmed().isEmpty()) {
         m_resetTimer.start();
         m_manager->launchQuery(queryString, m_runner);
         setQuerying(true);