Attempt to fix bug #17771 with segfault if "C-h h" is interrupted.

 src/alloc.c (cleanup_vector): Don't dereference a font driver
 pointer if it is NULL.

2 files changed, 15 insertions, 3 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 3468cea6159..87b9b32510e 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,8 @@
+2014-06-13  Eli Zaretskii  <eliz@gnu.org>
+
+        * alloc.c (cleanup_vector): Don't dereference a font driver
+        pointer if it is NULL.  (Bug#17771)
+
 2014-06-11  Eli Zaretskii  <eliz@gnu.org>
 
         * xdisp.c (set_cursor_from_row): Fix an off-by-one error when
diff --git a/src/alloc.c b/src/alloc.c
index 12b3d4ba165..a3f3f5478cb 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -2924,9 +2924,16 @@ cleanup_vector (struct Lisp_Vector *vector)
       && ((vector->header.size & PSEUDOVECTOR_SIZE_MASK)
           == FONT_OBJECT_MAX))
     {
-      /* Attempt to catch subtle bugs like Bug#16140.  */
-      eassert (valid_font_driver (((struct font *) vector)->driver));
-      ((struct font *) vector)->driver->close ((struct font *) vector);
+      struct font_driver *drv = ((struct font *) vector)->driver;
+
+      /* The font driver might sometimes be NULL, e.g. if Emacs was
+         interrupted before it had time to set it up.  */
+      if (drv)
+        {
+          /* Attempt to catch subtle bugs like Bug#16140.  */
+          eassert (valid_font_driver (drv));
+          drv->close ((struct font *) vector);
+        }
     }
 }