The test should be run using the wrapper run-tests.sh. This links
the tests into the normal notmuch TEST_DIRECTORY and runs them from
there. After the test is complete then the links are removed.
If the user pressed return on the end result status line it gave a
blank message. Modify the function notmuch-pick-get-message-id to
return nil rather than an empty message-id in this case to fix this.
This also fixes a bug in the (lack of) quoting of the id string.
