FIX: union/skip not working correctly in some cases

resolves: Oldes/Rebol-issues#2520

Author: Oldes

src/core/t-map.c

@@ -170,7 +170,7 @@
 
 	// Append new value the target series:
 	if (mode > 1) {
-		hashes[hash] = SERIES_TAIL(series)+1;
+		hashes[hash] = (SERIES_TAIL(series) / wide) +1;
 		//Debug_Num("hash:", hashes[hash]);
 		Append_Series(series, (REBYTE*)key, wide);
 		//Dump_Series(series, "hash");

src/tests/units/series-test.r3

@@ -2162,6 +2162,15 @@ Rebol [
 --test-- "union with none and unset"
 	--assert [#[none] #[unset]] = union [#[none]] [#[unset]]
 
+--test-- "union/skip"
+	;@@ https://github.com/Oldes/Rebol-issues/issues/2520
+	--assert (union      [a 1 b 2] [a 1 b 2]          ) == [a 1 b 2]
+	--assert (union/skip [b 1 b 2] [b 1 b 2] 2        ) == [b 1]
+	--assert (union/skip [b 1 b 2] [b 2 b 2] 2        ) == [b 1]
+	--assert (union/skip [b 2 b 2] [b 2 b 2] 2        ) == [b 2]
+	--assert (union/skip [a 1 b 2] [a 1 b 2] 2        ) == [a 1 b 2]
+	--assert (union/skip ["a" 1 "b" 2] ["a" 1 "b" 2] 2) == ["a" 1 "b" 2]
+
 --test-- "union/skip with negative skip"
 	;@@ https://github.com/Oldes/Rebol-issues/issues/736
 	--assert all [