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;
 	}

tests/engine_test.c

@@ -454,6 +454,16 @@ engine_commit_contract(struct ct *t)
 	CT_EQ_INT(t, 0, im.nkouho);
 	CT_EQ_INT(t, -1, im.sel);
 
+	/* Without candidates the movement keys commit like any other. */
+	init();
+	im.l = getlang(LangKO);
+	sclear(&com);
+	if(!typekeys(t, "dy", &com))
+		return;
+	CT_CHECK(t, !keystroke(Kdown, 0, &com));
+	checkstr(t, "arrow commit", "요", &com);
+	CT_EQ_INT(t, 0, im.pre.n);
+
 	init();
 	im.l = getlang(LangJP);
 	sclear(&com);