Fix the OPL-update script (or really the download-OPL-metadata-releas…

…e.pl script)

The `download-OPL-metadata-release.pl` is extracting the downloaded
metadata release to the wrong directory, and so the rest of the script
fails.  It fails quietly, and doesn't actually restore any tables. So a
die statement was added to cover this case.

bin/download-OPL-metadata-release.pl

@@ -56,10 +56,13 @@ BEGIN
 
 my $arch = Archive::Tar->new($releaseFile);
 die "An error occurred while creating the tar file: $releaseFile" unless $arch;
-$arch->setcwd($path);
-$arch->extract();
+$arch->setcwd($ce->{webworkDirs}{tmp});
+$arch->extract;
 die "There was an error extracting the metadata release: $arch->error" if $arch->error;
 
+die "The downloaded archive did not contain the expected files."
+	unless -e "$ce->{webworkDirs}{tmp}/webwork-open-problem-library";
+
 # Copy the json files into htdocs.
 for (glob("$ce->{webworkDirs}{tmp}/webwork-open-problem-library/JSON-SAVED/*.json")) {
 	copy($_, "$ce->{webworkDirs}{htdocs}/DATA/") or die "Copy $_ to $ce->{webworkDirs}{htdocs}/DATA/ failed: $!";