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.

1 files changed, 10 insertions, 3 deletions

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);
+	}
     }
 }