code-style: slight cleanups

* put TOP_STATUSBAR under the HAVE_LIBFONTS guard
* change get_win_title param to take unsigned char ptr
* init UTF8_STRING like other atoms

nsxiv.h

@@ -380,6 +380,7 @@ enum {
 	ATOM__NET_WM_STATE,
 	ATOM__NET_WM_PID,
 	ATOM__NET_WM_STATE_FULLSCREEN,
+	ATOM_UTF8_STRING,
 	ATOM_COUNT
 };