wcap-snapshot: add return value

Distro build with rpmlint aborts due to missing exit status.
diff --git a/wcap/wcap-snapshot.c b/wcap/wcap-snapshot.c
index 660a027..01df7a2 100644
--- a/wcap/wcap-snapshot.c
+++ b/wcap/wcap-snapshot.c
@@ -80,4 +80,5 @@
 	       decoder->width, decoder->height, i);
 
 	wcap_decoder_destroy(decoder);
+	return EXIT_SUCCESS;
 }