fix(engine): movement keys without candidates commit the pending text

Up, Down, PageUp and PageDown with a composition pending and nothing to
move through returned the key uneaten but left the text pending, so the
client moved its cursor and reset the context: the pending Korean
syllable vanished, where Left or Home would have committed it. Let them
fall through to the special-key path that commits and passes the key.

strans.c

@@ -671,9 +671,7 @@ transition(u32int ks, u32int mod, Str *com)
 	if(search.lang)
 		return searchkey(ks, mod, com);
 	n = movedelta(ks);
-	if(n != 0){
-		if(im.nkouho == 0)
-			return 0;
+	if(n != 0 && im.nkouho != 0){
 		movekouho(n);
 		return 1;
 	}