[libxml2] Fix "xmllint -"

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 8be44aeb16704f5f8a1355523b72402d7bb99b16
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Mon Feb 7 20:54:33 2022 +0100

    Fix "xmllint -"
    
    Short-lived regression from commit d12be00d.

 xmllint.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/xmllint.c b/xmllint.c
index 4d541d9b..f24aa0e9 100644
--- a/xmllint.c
+++ b/xmllint.c
@@ -3198,7 +3198,7 @@ main(int argc, char **argv) {
     LIBXML_TEST_VERSION
 
     for (i = 1; i < argc ; i++) {
-       if (argv[i][0] != '-')
+       if (argv[i][0] != '-' || argv[i][1] == 0)
            continue;
 
        if ((!strcmp(argv[i], "-debug")) || (!strcmp(argv[i], "--debug")))