gpg: Fix a NULL-deref for invalid input data.
* g10/mainproc.c (proc_encrypted): Take care of canceled passpharse entry.
(backported from commit 32e85668b82f6fbcb824eea9548970804fb41d9e)
- GnuPG-bug-id: T1761
- Signed-off-by: Werner Koch <wk@gnupg.org>