gpg: Fix possible out-of-bounds read in is_armored.
* g10/armor.c (check_input): Call is_armored only if LEN >= 2. (unarmor_pump): Use a 2 byte buffer for is_armored.
- Fixes-commit: 605276ef8cd449bfd574ae6c498fa5d7d265c5c7
- Signed-off-by: Werner Koch <wk@gnupg.org>