mail/horde-imp: address ZDI-20-1051 / ZDI-CAN-10436

PR: 267049
Approved by: maintainer’s time-out
Obtained from: https://github.com/horde/imp/pull/10/files
Fixes: Address ZDI-20-1051 / ZDI-CAN-10436
MFH: 2022Q4
Security: https://www.zerodayinitiative.com/advisories/ZDI-20-1051/