Bug 4124

Evince viewer crashes due to cairo_hash_string not handling the case when c == NULL.

This is the crash i get

(gdb) r ~/test.pdf
Starting program: /usr/local/bin/evince ~/test.pdf
[Thread debugging using libthread_db enabled]
[New Thread 16384 (LWP 11075)]
[New Thread 32769 (LWP 11078)]
[New Thread 16386 (LWP 11079)]

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 16386 (LWP 11079)]
0xb70f292e in _cairo_hash_string (c=0x0) at cairo-cache.c:516
516             hash = ((hash << 5) + hash) + *c++;
(gdb) p hash
$1 = 5381
(gdb) p c
$2 = 0x0
(gdb) where
#0  0xb70f292e in _cairo_hash_string (c=0x0) at cairo-cache.c:516
#1  0xb7105015 in _cairo_ft_unscaled_font_init_key (key=0x830fc88, filename=0x0,
id=0) at cairo-ft-font.c:260
#2  0xb7105077 in _cairo_ft_unscaled_font_init (unscaled=0x830fc88,
filename=0x0, id=137428104, face=0x830dd80) at cairo-ft-font.c:301
#3  0xb71083f3 in cairo_ft_font_face_create_for_ft_face (face=0x830fc88,
load_flags=10) at cairo-ft-font.c:426
#4  0xb7179b11 in CairoFont::CairoFont () from /usr/local/lib/libpoppler.so.0
#5  0xb717a2ea in CairoFontEngine::getFont () from /usr/local/lib/libpoppler.so.0
#6  0xb717ac34 in CairoOutputDev::updateFont () from /usr/local/lib/libpoppler.so.0
#7  0xb7193281 in Gfx::doShowText () from /usr/local/lib/libpoppler.so.0
#8  0xb7193408 in Gfx::opShowSpaceText () from /usr/local/lib/libpoppler.so.0
#9  0xb718c046 in Gfx::execOp () from /usr/local/lib/libpoppler.so.0
#10 0xb718c226 in Gfx::go () from /usr/local/lib/libpoppler.so.0
#11 0xb718c656 in Gfx::display () from /usr/local/lib/libpoppler.so.0
#12 0xb71cd816 in Page::displaySlice () from /usr/local/lib/libpoppler.so.0
#13 0xb734f0e1 in poppler_page_render_to_pixbuf () from
/usr/local/lib/libpoppler-glib.so.0
#14 0x0808c1ec in pdf_document_get_type ()
#15 0x0808a44d in ev_document_render_pixbuf ()
#16 0x08060aa5 in ev_job_render_run ()
#17 0x0805f15e in ev_document_types_add_filters ()
#18 0x0805f2b0 in ev_document_types_add_filters ()
#19 0xb6df11f9 in g_thread_create_proxy (data=0xb6e31188) at gthread.c:564
#20 0xb7359d03 in pthread_start_thread () from /lib/libpthread.so.0
#21 0xb7359d7f in pthread_start_thread_event () from /lib/libpthread.so.0
#22 0xb6b13767 in __clone () from /lib/libc.so.6