Prevent using --list-rules and --list-vars together

There's no check preventing `--list-rules` and `--list-vars` from being
passed simultaneously. If both are set, `--list_rules` wins silently
because of the `if/else if` chain. We will print an error message in
this situation.

Author: jan-cerny

tests/API/XCCDF/unittests/test_list_vars.sh

@@ -25,4 +25,10 @@ grep -q "\-\-list-vars option requires \-\-profile" $stderr
 :> $stdout
 :> $stderr
 
+# Test 3: --list-vars with --list-rules produces an error
+$OSCAP info --profile $p1 --list-vars --list-rules $ds > $stdout 2> $stderr && exit 1 || true
+grep -q "The \-\-list-rules and \-\-list-vars options can't be used at the same time." $stderr
+:> $stdout
+:> $stderr
+
 rm -f $stdout $stderr

utils/oscap-info.c

@@ -923,6 +923,11 @@ bool getopt_info(int argc, char **argv, struct oscap_action *action)
 		return false;
 	}
 
+	if (action->list_rules && action->list_vars) {
+		oscap_module_usage(action->module, stderr, "The --list-rules and --list-vars options can't be used at the same time.\n");
+		return false;
+	}
+
 	if (optind >= argc) {
 		oscap_module_usage(action->module, stderr, "SCAP file needs to be specified!\n");
 		return false;