The API states that the related functions must return NULL if the function
called (get the parent tray, or get the parent entry) is invalid for this
menu. Initialising the fields to NULL makes that API correct for Windows.
The test/testtray program would crash on Windows when adding any item and then removing it, because a submenu's parent_entry field was not set.
Additionally, I noticed that some extraneous code copied from the {G,S}etTrayEntryChecked made {G,S}etTrayEntryEnabled work only for checkboxes, which is not the desired behavior.
Both issues were fixed in this commit.
SDL_CreateTray now respects SDL_HINT_WINDOWS_INTRESOURCE_ICON_SMALL
and SDL_HINT_WINDOWS_INTRESOURCE_ICON hints and uses the specified icon
as the tray icon.
SDL_HINT_QUIT_ON_LAST_WINDOW_CLOSE will not fire if there are active tray icons. This impacts only applications that create tray icons, and that at least one icon outlives the last visible top-level window. SDL_EVENT_QUIT will fire when the last active tray is destroyed if there are no active windows.
