Fix cluster -? to actually print usage instead of error on macOS

Towards https://gitlab.com/graphviz/graphviz/-/issues/1852.

diff --git a/cmd/gvmap/cluster.c b/cmd/gvmap/cluster.c
index e5232bac96a042ac4ea2a4f56ab7889231cf4b87..a7fcdf7c98a64c17c81aa0a259c91d2eb67e6ca3 100644 (file)
--- a/cmd/gvmap/cluster.c
+++ b/cmd/gvmap/cluster.c
@@ -120,7 +120,7 @@ static void init(int argc, char *argv[], opts_t* opts) {
       Verbose = 1;
       break;
     case '?':
-      if (optopt == '\0')
+      if (optopt == '\0' || optopt == '?')
        usage(cmd, 0);
       else {
        fprintf(stderr, " option -%c unrecognized\n",