[libxml2] Don't call printf with NULL string in runtest.c

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 6c91dd94959c94ee139e870843f285fcb22fc55c
Author: Daniel Richard G <skunk iSKUNK ORG>
Date:   Thu Aug 1 15:01:47 2019 +0200

    Don't call printf with NULL string in runtest.c
    
    Avoids undefined behavior causing problems on HP-UX and Solaris.
    
    Closes #78.

 runtest.c | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/runtest.c b/runtest.c
index b1c30d85..13e36a49 100644
--- a/runtest.c
+++ b/runtest.c
@@ -880,6 +880,8 @@ internalSubsetDebug(void *ctx ATTRIBUTE_UNUSED, const xmlChar *name,
     callbacks++;
     if (quiet)
        return;
+    if (name == NULL)
+        name = BAD_CAST "(null)";
     fprintf(SAXdebug, "SAX.internalSubset(%s,", name);
     if (ExternalID == NULL)
        fprintf(SAXdebug, " ,");