Catch errors early and exit, such as when best chain is still activating

contrib/checkpoints.pl

@@ -1,5 +1,5 @@
 #!/usr/bin/perl
-# Copyright 2019 The Hush developers
+# Copyright 2019-2020 The Hush developers
 # Released under the GPLv3
 use warnings;
 use strict;
@@ -12,6 +12,10 @@ my $gethash = "$hush getblockhash";
 my $stride  = shift || 1000;
 my $count   = 0;
 my $blocks  = qx{$hush getblockcount};
+if($?) {
+    print "ERROR, exiting...\n";
+    exit 1;
+}
 my $prev    = $blocks - $perday;
 my $last    = 0;
 my $now     = time();