Fix FileSystemDock thumbnails sometimes not displaying

There were (at least) three cases where thumbnails would not display, if they were generated while the FileSystemDock was not visible:
	- current_path == "Favorites", due to p_path not starting with "Favorites"
	- current_path == "res://", due to current_path having last "/" trimmed for comparison
	- current_path pointing to a selected file instead of folder, since it no longer matches p_path's base directory

This change removes the current_path and is_visible_in_tree checks when determining whether to update the file's icon.

Fixes #90801
Fixes #91432

editor/filesystem_dock.cpp

@@ -778,7 +778,7 @@ void FileSystemDock::navigate_to_path(const String &p_path) {
 }
 
 void FileSystemDock::_file_list_thumbnail_done(const String &p_path, const Ref<Texture2D> &p_preview, const Ref<Texture2D> &p_small_preview, const Variant &p_udata) {
-	if ((file_list_vb->is_visible_in_tree() || current_path.trim_suffix("/") == p_path.get_base_dir()) && p_preview.is_valid()) {
+	if (p_preview.is_valid()) {
 		Array uarr = p_udata;
 		int idx = uarr[0];
 		String file = uarr[1];