tests: destroy screenshooter

Fixes a leak found by ASan in alpha-blending-test.

Direct leak of 160 byte(s) in 2 object(s) allocated from:
    #0 0x7f511fe11518 in calloc (/lib/x86_64-linux-gnu/libasan.so.5+0xe9518)
    #1 0x7f511fc76373 in zalloc ../../git/wayland/src/wayland-private.h:232
    #2 0x7f511fc76373 in proxy_create ../../git/wayland/src/wayland-client.c:422
    #3 0x7f511fc79dcc in create_outgoing_proxy ../../git/wayland/src/wayland-client.c:651
    #4 0x7f511fc79dcc in wl_proxy_marshal_array_constructor_versioned ../../git/wayland/src/wayland-client.c:736
    #5 0x7f511fc7b17b in wl_proxy_marshal_constructor_versioned ../../git/wayland/src/wayland-client.c:873
    #6 0x5583e5348f43 in wl_registry_bind /home/pq/local/include/wayland-client-protocol.h:1165
    #7 0x5583e534cfbe in handle_global ../../git/weston/tests/weston-test-client-helper.c:800
    #8 0x7f511f34b8ed in ffi_call_unix64 (/lib/x86_64-linux-gnu/libffi.so.6+0x68ed)

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

tests/weston-test-client-helper.c

@@ -1069,6 +1069,8 @@ client_destroy(struct client *client)
 		free(client->test);
 	}
 
+	if (client->screenshooter)
+		weston_screenshooter_destroy(client->screenshooter);
 	if (client->wl_shm)
 		wl_shm_destroy(client->wl_shm);
 	if (client->wl_compositor)