Fix the PG Problem Editor for files that have spaces in the filename.

The glob in the `getBackupTimes` method needs special quoting to handle
spaces in filenames.

To test this try to edit a pg problem with spaces in the filename.  On
develop the editor won't open, and you get an exception screen.  With
this pull request it will work of course.

Author: drgrice1

lib/WeBWorK/ContentGenerator/Instructor/PGProblemEditor.pm

@@ -566,7 +566,7 @@ sub getFilePaths ($c) {
 
 sub getBackupTimes ($c) {
 	my $backupBasePath = $c->{backupBasePath};
-	my @files          = glob("$backupBasePath*");
+	my @files          = glob(qq("$backupBasePath*"));
 	return unless @files;
 	return reverse(map { $_ =~ s/$backupBasePath//r } @files);
 }