Don't run CDB update_detector more than once (#14214)

builtin/mainmenu/content/update_detector.lua

@@ -28,6 +28,13 @@ end
 
 local has_fetched = false
 local latest_releases
+do
+	local tmp = core.get_once("cdb_latest_releases")
+	if tmp then
+		latest_releases = core.deserialize(tmp, true)
+		has_fetched = latest_releases ~= nil
+	end
+end
 
 
 local function fetch_latest_releases()
@@ -89,8 +96,9 @@ local function fetch()
 			has_fetched = false
 			return
 		end
-
 		latest_releases = lowercase_keys(releases)
+		core.set_once("cdb_latest_releases", core.serialize(latest_releases))
+
 		if update_detector.get_count() > 0 then
 			local maintab = ui.find_by_name("maintab")
 			if not maintab.hidden then

doc/menu_lua_api.md

@@ -38,7 +38,9 @@ Functions
 ---------
 
 * `core.start()`
+  * start game session
 * `core.close()`
+  * exit engine
 * `core.get_min_supp_proto()`
   * returns the minimum supported network protocol version
 * `core.get_max_supp_proto()`
@@ -53,6 +55,10 @@ Functions
   * Android only. Shares file using the share popup
 * `core.get_version()` (possible in async calls)
   * returns current core version
+* `core.set_once(key, value)`:
+  * save a string value that persists even if menu is closed
+* `core.get_once(key)`:
+  * get a string value saved by above function, or `nil`