enforsed compilation with -W -Werror

diff --git a/skeletons/GraphicString.c b/skeletons/GraphicString.c
index 5c89685..412f3c7 100644
--- a/skeletons/GraphicString.c
+++ b/skeletons/GraphicString.c
@@ -23,5 +23,6 @@
 	  / sizeof(asn1_DEF_GraphicString_tags[0]),
 	1,	/* Single UNIVERSAL tag may be implicitly overriden */
 	-1,	/* Both ways are fine */
+	0	/* No specifics */
 };