gpg: Allow decryption using several passphrases in may cases.
* g10/mainproc.c (symkey_decrypt_seskey): Check for a valid algorithm. (proc_symkey_enc): Clear passpharse on error from above function.
This does not work reliable as stated in bug 3795 but we can try to
fix ~95% of all cases. The real fix is to use AEAD which will come