[libxslt] Fix UTF-8 check in str:padding

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 8418a0b8307f1a5df3c9131498f73b98e482a1d6
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Mon May 22 13:47:12 2017 +0200

    Fix UTF-8 check in str:padding
    
    Make sure that all arguments are popped before checking for UTF-8
    validity. Improves upon recent commit 1785d11.

 libexslt/strings.c |    9 +++++----
 1 files changed, 5 insertions(+), 4 deletions(-)
---
diff --git a/libexslt/strings.c b/libexslt/strings.c
index b967a36..d55ec44 100644
--- a/libexslt/strings.c
+++ b/libexslt/strings.c
@@ -361,6 +361,11 @@ exsltStrPaddingFunction (xmlXPathParserContextPtr ctxt, int nargs) {
        str = xmlXPathPopString(ctxt);
        str_len = xmlUTF8Strlen(str);
        str_size = xmlStrlen(str);
+    }
+
+    floatval = xmlXPathPopNumber(ctxt);
+
+    if (str_len <= 0) {
         if (str_len < 0) {
             xsltGenericError(xsltGenericErrorContext,
                              "exsltStrPaddingFunction: invalid UTF-8\n");
@@ -368,16 +373,12 @@ exsltStrPaddingFunction (xmlXPathParserContextPtr ctxt, int nargs) {
             xmlFree(str);
             return;
         }
-    }
-    if (str_len == 0) {
        if (str != NULL) xmlFree(str);
        str = xmlStrdup((const xmlChar *) " ");
        str_len = 1;
        str_size = 1;
     }
 
-    floatval = xmlXPathPopNumber(ctxt);
-
     if (xmlXPathIsNaN(floatval) || floatval < 0.0) {
         number = 0;
     } else if (floatval >= 100000.0) {