make it possible to manually select untrusted PGP keys

Fixes a bug in method "selectKeys", when manually selecting one or more
keys which are not marked as trusted. Method "selectKeys" is only called
from method "getEncryptionKeys" in lines: 1656, 1696

(patch written by kolAflash <kolAflash@kolahilft.de>, sponserd by me)

BUG: 328311
FIXED-IN: 4.12.2
REVIEW: 115182