FIX: COPY/part on VECTOR is silently ignored

fixes: metaeducation/rebol-issues#2399

Author: Oldes

src/core/t-vector.c

@@ -683,6 +683,7 @@ void Set_Vector_Row(REBSER *ser, REBVAL *blk)
 	REBSER *ser;
 	REBSER *blk;
 	REBVAL *val;
+	REBINT	len;
 
 	type = Do_Series_Action(action, value, arg);
 	if (type >= 0) return type;
@@ -742,7 +743,8 @@ void Set_Vector_Row(REBSER *ser, REBVAL *blk)
 		return R_RET;
 
 	case A_COPY:
-		ser = Copy_Series(vect);
+		len = Partial(value, 0, D_ARG(3), 0); // Can modify value index.
+		ser = Copy_Series_Part(vect, VAL_INDEX(value), len);
 		ser->size = vect->size; // attributes
 		SET_VECTOR(value, ser);
 		break;

src/tests/units/vector-test.r3

@@ -357,4 +357,15 @@ Rebol [
 
 ===end-group===
 
+===start-group=== "VECTOR copy"
+
+--test-- "COPY/PART"
+	;@@ https://github.com/rebol/rebol-issues/issues/2399
+	v: #[ui16! [1 2 3 4]]
+	--assert           2 = length? copy/part v 2
+	--assert #{01000200} = to-binary copy/part v 2
+	--assert #{03000400} = to-binary copy/part skip v 2 2
+
+===end-group===
+
 ~~~end-file~~~