add error code

AWError.h

@@ -40,6 +40,7 @@
                                                       \
   XX(ERR_INVALID_LENGTH, "Invalid length")            \
   XX(ERR_INVALID_DATA, "Invalid data")                \
+  XX(ERR_INVALID_INDEX, "Invalid index")              \
   /* unknown error */                                 \
   XX(ERR_UNKNOWN, "Unexpected error occurred")