* rsvg-paint-server.c: (rsvg_paint_server_lin_grad_render),
	(rsvg_paint_server_rad_grad_render): Prevent empty gradients
	from crashing librsvg.

	* rsvg.c: (rsvg_start_svg): Prevent huge image sizes from causing
	a core dump by doing overflow checking and using g_try_malloc
	instead of g_new.

	* test-64684-1.svg:
	* test-64684-2.svg:
	Add some more test cases.