OP_CODESEPARATOR bug fix

Off by one bug, the subscript does not include the opcode separator itself, so the slice of the script should be from just after the op code separator - not before.

This took about 16 hours to find 😫

Signed-off-by: Darren Kellenschwiler <deggen@kschw.com>

bscript/interpreter/thread.go

@@ -505,7 +505,11 @@ func (t *thread) SetStack(data [][]byte) {
 
 // subScript returns the script since the last OP_CODESEPARATOR.
 func (t *thread) subScript() ParsedScript {
-	return t.scripts[t.scriptIdx][t.lastCodeSep:]
+	skip := 0
+	if t.lastCodeSep > 0 {
+		skip = t.lastCodeSep + 1 // +1 to skip the opcode separator itself
+	}
+	return t.scripts[t.scriptIdx][skip:]
 }
 
 // checkHashTypeEncoding returns whether the passed hashtype adheres to