[libxml2] Fix test in configure.ac

[Nick Wellnhofer <nwellnhof src gnome org>]

commit e47df37be9f602cd6ad51b250fbcd7ffa20c136f
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Sun Sep 4 00:46:32 2022 +0200

    Fix test in configure.ac
    
    Broken in commit b4847d60.

 configure.ac | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/configure.ac b/configure.ac
index 7dbef1b9..d58898d1 100644
--- a/configure.ac
+++ b/configure.ac
@@ -788,7 +788,7 @@ fi
 AC_SUBST(WITH_OUTPUT)
 AM_CONDITIONAL(WITH_OUTPUT_SOURCES, test "$WITH_OUTPUT" = "1")
 
-if test "$WITH_ICONV" != "1" && "$with_iso8859x" = "no" ; then
+if test "$WITH_ICONV" != "1" && test "$with_iso8859x" = "no" ; then
     echo Disabling ISO8859X support
     WITH_ISO8859X=0
 else