configure: fix return value from check_header

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@17695 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

configure

@@ -574,7 +574,8 @@ check_header(){
     log check_header "$@"
     header=$1
     shift
-    check_cpp "$@" <<EOF && enable_safe $header || disable_safe $header
+    disable_safe $header
+    check_cpp "$@" <<EOF && enable_safe $header
 #include <$header>
 int x;
 EOF