engine: a search just begun shows itself

Ctrl+E and Ctrl+H gave no sign until a key produced candidates; with
nothing pending the popup even went away.  An empty search now shows
☺ or 漢 in the popup, so the user knows the next keys are a query.

tests/engine_test.c

@@ -1359,6 +1359,8 @@ engine_emoji_single_candidate(struct ct *t)
 	CT_CHECK(t, keystroke('e', Mctrl, &com));
 	CT_CHECK(t, search.lang);
 	CT_EQ_INT(t, LangKO, im.l->lang);
+	if(CT_CHECK(t, draindraw(&dc) > 0))
+		checkstr(t, "empty search shows itself", "☺", &dc.pre);
 	if(typekeys(t, "alpha", &com)){
 		checkstr(t, "no automatic commit", "", &com);
 		checkstr(t, "raw English query", "alpha", &search.text);