Fix FTBFS due to invalid pointer in iconv function

Signed-off-by: François Andriot <francois.andriot@thalesgroup.com>
(cherry picked from commit eb8f32b893)

kernel/kls_xcf/xcf2pnm/xcf-general.c

@@ -132,7 +132,7 @@ xcfString(uint32_t ptr,uint32_t *after)
     else
       while(1) {
         char *buffer = xcfmalloc(targetsize) ;
-        const char *inbuf = utf8master ;
+        char *inbuf = utf8master ;
         char *outbuf = buffer ;
         size_t incount = length ;
         size_t outcount = targetsize ;