Trap ET_INVALID

fix CC#1756
Without this commit:

>> reduce reduce [:self]
REBOL system error #1101
Program terminated abnormally
This should never happen

With this commit:
>> reduce reduce [:self]
** Script error: frame! has no value
** Where: reduce
** Near: reduce reduce [:self]

Author: zsx

src/core/c-do.c

@@ -968,6 +968,10 @@ x*/	static REBINT Do_Args_Light(REBVAL *func, REBVAL *path, REBSER *block, REBCN
 	case ET_END:
 		 return END_FLAG;
 
+	case ET_INVALID:
+		 Trap1(RE_NO_VALUE, value);
+		 break;
+
 	default:
 		//Debug_Fmt("Bad eval: %d %s", VAL_TYPE(value), Get_Type_Name(value));
 		Crash(RP_BAD_EVALTYPE, VAL_TYPE(value));