i3bar: Fix pixel offset calculation in dual-head

Long description:

When running i3bar on a dual-head display with workspaces enabled in i3bar's
config, the second monitor wouldn't use a correct x position offset and
would draw its label too close to the screen's edge.  In comparison to the
first monitor, this is inconsistent because that starts with a pixel offset
of 1.

To apply this patch, use:
curl http://cr.i3wm.org/patch/160/raw.patch | git am

@@ -1557,7 +1557,7 @@ void reconfig_windows(void) {

  */

 void draw_bars(bool unhide) {

     DLOG("Drawing Bars...\n");

-    int i = 1;

+    int i = 0;

     refresh_statusline();

@@ -1621,6 +1621,7 @@ void draw_bars(bool unhide) {

         i3_ws *ws_walk;

+	i++;

         TAILQ_FOREACH(ws_walk, outputs_walk->workspaces, tailq) {

             DLOG("Drawing Button for WS %s at x = %d, len = %d\n", i3string_as_utf8(ws_walk->name), i, ws_walk->name_width);

             uint32_t fg_color = colors.inactive_ws_fg;