test: Fix missing erase-buffer in emacs test

The first subprocess error exit code test assumed the *Notmuch errors*
buffer would be empty.  Rather than assuming, make it so.

diff --git a/test/emacs b/test/emacs
index 5bc3efcc6a87dc65b19031d489a804cc52b5fa2e..05295af8afc3f2e90887cb1a4ce85581f0a0a382 100755 (executable)
--- a/test/emacs
+++ b/test/emacs
@@ -864,6 +864,8 @@ EOF
 chmod a+x notmuch_fail
 test_emacs "(let ((notmuch-command \"$PWD/notmuch_fail\"))
               (with-current-buffer \"*Messages*\" (erase-buffer))
+              (with-current-buffer (get-buffer-create \"*Notmuch errors*\")
+                 (erase-buffer))
               (notmuch-search \"tag:inbox\")
               (notmuch-test-wait)
               (with-current-buffer \"*Messages*\"
@@ -893,7 +895,8 @@ EOF
 chmod a+x notmuch_fail
 test_emacs "(let ((notmuch-command \"$PWD/notmuch_fail\"))
               (with-current-buffer \"*Messages*\" (erase-buffer))
-              (with-current-buffer \"*Notmuch errors*\" (erase-buffer))
+              (with-current-buffer (get-buffer-create \"*Notmuch errors*\")
+                 (erase-buffer))
               (notmuch-search \"tag:inbox\")
               (notmuch-test-wait)
               (with-current-buffer \"*Messages*\"