bdfReadCharacters: bailout if a char's bitmap cannot be read
Previously would charge on ahead with a NULL pointer in ci->bits, and
then crash later in FontCharInkMetrics() trying to access the bits.
(From OE-Core rev: 2c7a15a074501beb6b8a4c7bdf30604b1a432a6b)
Signed-off-by: Li Zhou <li.zhou@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>