emacs: Fix exception when fetching empty or unconfigured settings

When "notmuch config" is called with the name of an empty or
unconfigured setting, it prints nothing (not even a new line).
Previously, `notmuch-config-get' assumed it would always print a
newline.  As a result, when `notmuch-config-get' was called with the
name of an empty of unconfigured setting, it would attempt to
(substring "" 0 -1) to strip the newline, which would fail with a
(args-out-of-range "" 0 -1) exception.

Fix this by only stripping the newline if there actually is one.

1 files changed, 7 insertions, 2 deletions

diff --git a/emacs/notmuch-lib.el b/emacs/notmuch-lib.el
index fa35fa9f..09110b53 100644
--- a/emacs/notmuch-lib.el
+++ b/emacs/notmuch-lib.el
@@ -198,8 +198,13 @@ on the command line, and then retry your notmuch command")))
 
 (defun notmuch-config-get (item)
   "Return a value from the notmuch configuration."
-  ;; Trim off the trailing newline
-  (substring (notmuch-command-to-string "config" "get" item) 0 -1))
+  (let* ((val (notmuch-command-to-string "config" "get" item))
+	 (len (length val)))
+    ;; Trim off the trailing newline (if the value is empty or not
+    ;; configured, there will be no newline)
+    (if (and (> len 0) (= (aref val (- len 1)) ?\n))
+	(substring val 0 -1)
+      val)))
 
 (defun notmuch-database-path ()
   "Return the database.path value from the notmuch configuration."