Refs #9120. Process events after the search is finished

After the file searching thread is finished, it emits some signals
which MWRunFiles needs to process before we can access the found files.
We are now doing that by calling QApplication::processEvent() after the
search process has finished.

Code/Mantid/MantidQt/MantidWidgets/src/MuonSequentialFitDialog.cpp

@@ -297,9 +297,12 @@ namespace MantidWidgets
     // Wait for file search to finish.
     while ( m_ui.runs->isSearching() )
     {
-      QApplication::instance()->processEvents();
+      QApplication::processEvents();
     }
 
+    // To process events from the finished thread
+    QApplication::processEvents();
+
     // Validate input fields
     if ( ! isInputValid() )
     {