add CS_ERR_DIET error code to report information irrelevant in diet engine
diff --git a/cs.c b/cs.c
index 96dd91d..4f561a1 100644
--- a/cs.c
+++ b/cs.c
@@ -131,6 +131,8 @@
 			return "Dynamic memory management uninitialized (CS_ERR_MEMSETUP)";
 		case CS_ERR_VERSION:
 			return "Different API version between core & binding (CS_ERR_VERSION)";
+		case CS_ERR_DIET:
+			return "Information irrelevant in diet engine (CS_ERR_DIET)";
 	}
 }