configure: more properly disable header when check_header_oc() fails

This should make no difference currently
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

configure

@@ -947,6 +947,7 @@ check_header_oc(){
     log check_header_oc "$@"
     header=$1
     shift
+    disable_safe $header
     {
        echo "#include <$header>"
        echo "int main(void) { return 0; }"