Mutt segfaults when backend storage is lost.

Issue

• Mutt segfaults when backend storage is lost.

mutt[20015]: segfault at 0000000000000010 rip 0000000000437e46 rsp 00007fff80a12220 error 6
mutt[20021]: segfault at 0000000000000010 rip 0000000000437e46 rsp 00007fff1f8ba4c0 error 6
mutt[20027]: segfault at 0000000000000010 rip 0000000000437e46 rsp 00007fff8811aee0 error 6

• /var/log/messages shows

Oct 28 13:52:10 hostname kernel: mutt[20362]: segfault at 0000000000000010 rip 0000000000437e46 rsp 00007fff9ebfa0f0 error 6
Oct 28 13:52:12 hostname kernel: mutt[20368]: segfault at 0000000000000010 rip 0000000000437e46 rsp 00007fff9588b5b0 error 6
Oct 28 13:52:13 hostname kernel: mutt[20374]: segfault at 0000000000000010 rip 0000000000437e46 rsp 00007fffa8882310 error 6