[3.x] `File.file_exists` and `Directory.file_exists` returns `false` under the `PackedData` filesystem when file exists

[Rubonnek]

Godot version

3.x at 5600be9

System information

Arch Linux

Issue description

On certain paths where a file exist, File.file_exists and Directory.file_exists return false depending on what filesystem is being accessed.
Even when the file exists, in line 183 below, Map<PathMD5, PackedFile>.find does not seem to work properly since it returns a null value.

godot/core/io/file_access_pack.h

Lines 181 to 186 in 5600be9

	FileAccess *PackedData::try_open_path(const String &p_path) {
	PathMD5 pmd5(p_path.md5_buffer());
	Map<PathMD5, PackedFile>::Element *E = files.find(pmd5);
	if (!E) {
	return nullptr; //not found
	}

The md5 path hashing and finding does not seem to work as expected.

Related Issues:

• Directory dir_exists fails on exported projects on subpaths & paths with more than 2 slashes in res` #37646

Steps to reproduce

1. Decompress file_exists_bug.zip and open with the Editor and run the project. You'll see the following output:

Checking path with res://
Path: res://autoload/singleton_manager/singletons/engine_data_forwarder_manager/forward_engine_data_node.gd
File.file_exists: True
Directory.file_exists: True
load() check: [GDScript:1269]
Checking path without res://
Path: autoload/singleton_manager/singletons/engine_data_forwarder_manager/forward_engine_data_node.gd
File.file_exists: True
Directory.file_exists: True
load() check: [GDScript:1272]

3. Decompress file_exists_bug_export.pck.zip and open with

godot --main-pack file_exists_bug_export.pck

And you'll get the following output -- note that File.file_exists and Directory.file_exists return false but Godot is still able to load the resource:

Checking path with res://
Path: res://autoload/singleton_manager/singletons/engine_data_forwarder_manager/forward_engine_data_node.gd
File.file_exists: False
Directory.file_exists: False
load() check: [GDScript:1266]
Checking path without res://
Path: autoload/singleton_manager/singletons/engine_data_forwarder_manager/forward_engine_data_node.gd
File.file_exists: False
Directory.file_exists: False
load() check: [GDScript:1269]

Minimal reproduction project

file_exists_bug.zip
file_exists_bug_export.pck.zip

[Flavelius]

May be related #43990 ? just interestingly inverse