Make xterm-mouse-event check whether the click event is valid

* lisp/xt-mouse.el (xterm-mouse-event): Defensively check against
a situation that shouldn't happen (but does) (bug#17378).

diff --git a/lisp/xt-mouse.el b/lisp/xt-mouse.el
index 2b9fab556e035651880e2a3ec43a2cec7a5728d6..362d29b943d74ad417bdb614f067117cdb8bdaf7 100644 (file)
--- a/lisp/xt-mouse.el
+++ b/lisp/xt-mouse.el
@@ -237,7 +237,10 @@ which is the \"1006\" extension implemented in Xterm >= 277."
                      (xterm-mouse--read-event-sequence extension))
                     (t
                      (error "Unsupported XTerm mouse protocol")))))
-    (when click
+    (when (and click
+               ;; In very obscure circumstances, the click may become
+               ;; invalid (see bug#17378).
+               (>= (nth 1 click) 0))
       (let* ((type (nth 0 click))
              (x    (nth 1 click))
              (y    (nth 2 click))