ubsan fixes for issues seen in libreoffice
...when opening an Impress presentation on GNOME/X11:
cairo-xlib-source.c:570:26: runtime error: left shift of 191 by 24 places cannot be represented in type 'int'
cairo-xlib-render-compositor.c:1852:17: runtime error: left shift of negative value -186
cairo-xlib-render-compositor.c:1853:17: runtime error: left shift of negative value -646
cairo-xlib-surface-shm.c:1157:43: runtime error: member access within null pointer of type 'cairo_xlib_shm_surface_t' (aka 'struct _cairo_xlib_shm_surface')
cairo-fixed-private.h:252:8: runtime error: left shift of negative value -146048