* test-loaders.c (main): Enable some tests which should work
	now.

	* io-wbmp.c (gdk_pixbuf__wbmp_image_load_increment): Detect
	invalid image dimensions and insufficient memory.

	* io-tga.c (try_preload): Detect invalid image dimensions.
	(gdk_pixbuf__tga_stop_load): Don't try to unref NULL pointers.

	* io-ico.c (DecodeHeader): Detect some invalid headers and
	don't segfault.