Write a start marker to the DB event table

If we fail to retrieve the title, then there is no title,
though this doesn't mean the same as "no window",
for which we have NULL.

wdmtg.c

@@ -303,7 +303,7 @@ x_window_title(xcb_window_t window)
 	GString *title;
 	if (!(title = x_text_property(window, gen.atom_net_wm_name))
 	 && !(title = x_text_property(window, XCB_ATOM_WM_NAME)))
-		return g_strdup("broken");
+		return g_strdup("");
 	return g_string_free(title, false);
 }
 
@@ -540,11 +540,16 @@ generator_init(void)
 	g_free(subpath);
 	g_key_file_free(kf);
 
+	// Write a start marker so that we can reliably detect interruptions
+	struct event *event = g_slice_new0(struct event);
+	event->timestamp = -1;
+	g_async_queue_push(g.queue, event);
+
+	update_current_window();
+
 	gint64 timeout_ms = timeout * 1000;
 	gen.idle_timeout.hi = timeout_ms >> 32;
 	gen.idle_timeout.lo = timeout_ms;
-
-	update_current_window();
 	set_idle_alarm(&gen.idle_alarm_inactive,
 		XCB_SYNC_TESTTYPE_POSITIVE_COMPARISON, gen.idle_timeout);