SIGSEGV in tests

[phodina]

Hi,
I'm packing this crate for GuixSD and when running the tests I get SIGSEGV. I'm linking against notmuch-0.32.2

However, this bug does not manifest always. In 1 out of 10 runs of the test suits roughly all the 62 tests pass.

cylon2p0@asgard /tmp/guix-build-rust-notmuch-0.6.0.drv-0/notmuch-0.6.0$ cargo test --release
    Finished release [optimized] target(s) in 0.06s
     Running target/release/deps/notmuch-bc3ad1a95961d23f

running 1 test
Error: Database path must be absolute.
test messages::tests::recurse ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

     Running target/release/deps/tests-997a732bb1a951ef

running 62 tests
test test_database::database::test_create_existing ... ok
test test_database::database::test_close ... ok
test test_database::database::test_drop_noclose ... ok
test test_database::messages::test_find_message_notfound ... ok
test test_database::database::test_version ... ok
test test_database::database::test_create_already_open ... ok
test test_database::database::test_path ... ok
test test_database::database::test_create ... ok
test test_database::database::test_close_drop ... ok

(process:18670): GLib-GObject-WARNING **: 23:33:52.437: cannot register existing type 'NotmuchFilterDiscardNonTerm'

(process:18670): GLib-GObject-CRITICAL **: 23:33:52.438: g_object_new_with_properties: assertion 'G_TYPE_IS_OBJECT (object_type)' failed
Found 4 total files (that's not much mail).
error: test failed, to rerun pass '--test tests'

Caused by:
  process didn't exit successfully: `/tmp/guix-build-rust-notmuch-0.6.0.drv-0/notmuch-0.6.0/target/release/deps/tests-997a732bb1a951ef` (signal: 11, SIGSEGV: invalid memory reference)
cylon2p0@asgard /tmp/guix-build-rust-notmuch-0.6.0.drv-0/notmuch-0.6.0$ Note: Ignoring non-mail file: /tmp/guix-build-rust-notmuch-0.6.0.drv-0/.tmp0ca6mW/notmuch-config
Processed 4 total files in almost no time.
Added 3 new messages to the database.
Found 4 total files (that's not much mail).
Found 4 total files (that's not much mail).
Found 4 total files (that's not much mail).
Note: Ignoring non-mail file: /tmp/guix-build-rust-notmuch-0.6.0.drv-0/.tmpqfzvOf/notmuch-config
Processed 4 total files in almost no time.
Added 3 new messages to the database.
Note: Ignoring non-mail file: /tmp/guix-build-rust-notmuch-0.6.0.drv-0/.tmpjYVStf/notmuch-config
Processed 4 total files in almost no time.
Added 3 new messages to the database.
Note: Ignoring non-mail file: /tmp/guix-build-rust-notmuch-0.6.0.drv-0/.tmpWrqbWI/notmuch-config
Processed 4 total files in almost no time.
Added 3 new messages to the database.