patch 8.2.4282: restricted mode requires the -Z command line option

Problem:    Restricted mode requires the -Z command line option.
Solution:   Use restricted mode when $SHELL ends in "nologin" or "false".
            (closes #9681)
diff --git a/src/option.c b/src/option.c
index 339ea42..03274a4 100644
--- a/src/option.c
+++ b/src/option.c
@@ -307,6 +307,17 @@
      */
     set_options_default(0);
 
+#ifdef UNIX
+    // Force restricted-mode on for "nologin" or "false" $SHELL
+    p = get_isolated_shell_name();
+    if (p != NULL)
+    {
+	if (fnamecmp(p, "nologin") == 0 || fnamecmp(p, "false") == 0)
+	    restricted = TRUE;
+	vim_free(p);
+    }
+#endif
+
 #ifdef CLEAN_RUNTIMEPATH
     if (clean_arg)
     {