swaybar: don't wl_display_roundtrip on each frame

This was the source of numerous bugs, from hotplug events not being
received to segfaults because wl_display_roundtrip was making the
bar process unplug events while blocking in an iteration over all
outputs.

swaybar/bar.c

@@ -558,6 +558,7 @@ void bar_run(struct swaybar *bar) {
 	}
 	while (1) {
 		event_loop_poll();
+		wl_display_flush(bar->display);
 	}
 }
 

swaybar/render.c

@@ -510,7 +510,6 @@ void render_frame(struct swaybar *bar, struct swaybar_output *output) {
 		// TODO: this could infinite loop if the compositor assigns us a
 		// different height than what we asked for
 		wl_surface_commit(output->surface);
-		wl_display_roundtrip(bar->display);
 	} else if (height > 0) {
 		// Replay recording into shm and send it off
 		output->current_buffer = get_next_buffer(bar->shm,
@@ -536,7 +535,6 @@ void render_frame(struct swaybar *bar, struct swaybar_output *output) {
 		wl_surface_damage(output->surface, 0, 0,
 				output->width, output->height);
 		wl_surface_commit(output->surface);
-		wl_display_roundtrip(bar->display);
 	}
 	cairo_surface_destroy(recorder);
 	cairo_destroy(cairo);