Cluster: abort loading nodes data if vars arguments are unbalanced.

See for reference PR #6337. Thanks to @git-hulk for spotting this.

src/cluster.c

@@ -138,6 +138,7 @@ int clusterLoadConfig(char *filename) {
         /* Handle the special "vars" line. Don't pretend it is the last
          * line even if it actually is when generated by Redis. */
         if (strcasecmp(argv[0],"vars") == 0) {
+            if (!(argc % 2)) goto fmterr;
             for (j = 1; j < argc; j += 2) {
                 if (strcasecmp(argv[j],"currentEpoch") == 0) {
                     server.cluster->currentEpoch =