test: fix "Stashing in notmuch-search" test when emacs is not available

If emacs is not available, test_expect_equal would be called with only
one argument.  The patch fixes this by quoting the (possibly empty)
$(cat OUTPUT) argument.

1 files changed, 1 insertions, 1 deletions

diff --git a/test/emacs b/test/emacs
index 198c27b0..3f8c72d3 100755
--- a/test/emacs
+++ b/test/emacs
@@ -412,7 +412,7 @@ test_emacs '(notmuch-search "id:\"bought\"")
         (yank)
 	    (test-output)'
 sed -i -e 's/^thread:.*$/thread:XXX/' OUTPUT
-test_expect_equal $(cat OUTPUT) "thread:XXX"
+test_expect_equal "$(cat OUTPUT)" "thread:XXX"
 
 test_begin_subtest 'Hiding message following HTML part'
 test_subtest_known_broken