properly close file streams and add info when report is saved

src/main/java/de/uni_hamburg/corpora/gui/GUI.java

@@ -200,8 +200,15 @@ public class GUI {
                 }
                 try {
                     if (overwrite) {
-                        new BufferedInputStream(new FileInputStream(reportFile))
-                                .transferTo(new BufferedOutputStream(new FileOutputStream(chooser.getSelectedFile())));
+                        BufferedInputStream bis = new BufferedInputStream(new FileInputStream(reportFile));
+                        BufferedOutputStream bos =
+                                new BufferedOutputStream(new FileOutputStream(chooser.getSelectedFile()));
+                        bis.transferTo(bos);
+                        bis.close();
+                        bos.close();
+                        JOptionPane.showMessageDialog(window,
+                                "Report saved as " + chooser.getSelectedFile().getPath() + ".",
+                                "Info", JOptionPane.INFORMATION_MESSAGE);
                     }
                 }
                 catch (IOException e) {