tag_client: Update screen workarea

This fixes the last failure in test-struts.lua.

Signed-off-by: Uli Schlachter <psychon@znc.in>

objects/tag.c

@@ -321,6 +321,7 @@ tag_client(lua_State *L, client_t *c)
     client_array_append(&t->clients, c);
     ewmh_client_update_desktop(c);
     banning_need_update();
+    screen_update_workarea(c->screen);
 
     tag_client_emit_signal(t, c, "tagged");
 }