### Tested versions

4.2.stable (exported only)

### System information

Linux

### Issue description

This line is the bug:

https://github.com/godotengine/godot/blob/a311a4b162364d032b03ddf2a0e603ba40615ad7/core/io/file_access_pack.cpp#L330

`p_length` is the buffer length provided by the user, but this line does not check if the result is bigger than the length of the file.

As a result, when user tries to get a buffer that is bigger than the file (something like `file.get_buffer(99999999)`), `file.get_position()` may be bigger than `file.get_length()`.

It doesn't break Godot directly, but breaks any calculations based on `get_position()`. For example, it breaks relative seeking.

There is another variable `t_read` which is checked and should probably be used instead:

https://github.com/godotengine/godot/blob/a311a4b162364d032b03ddf2a0e603ba40615ad7/core/io/file_access_pack.cpp#L324-L328

### Steps to reproduce

Since this is a bug in `FileAccessPack`, it is only reproducible in **exported** projects (something like `FileAccessUnix` doesn't have this bug, so it can't be reproduced in the editor).

To reproduce, try to `file.get_buffer(99999999)` and then use `file.get_position()` for something.

### Minimal reproduction project (MRP)

I made a simple script that attempts to make a relative seeking and breaks because of this bug:

[FileAccessPackTest.zip](https://github.com/godotengine/godot/files/13615040/FileAccessPackTest.zip)
return false;
}
void FileAccessPack::close() {
	f = Ref<FileAccess>();
}
FileAccessPack::FileAccessPack(const String &p_path, const PackedData::PackedFile &p_file) :
		pf(p_file),
		f(FileAccess::open(pf.pack, FileAccess::READ)) {
	ERR_FAIL_COND_MSG(f.is_null(), "Can't open pack-referenced file '" + String(pf.pack) + "'.");
	f->seek(pf.offset);
	off = pf.offset;
	if (pf.encrypted) {
		Ref<FileAccessEncrypted> fae;
		fae.instantiate();
		ERR_FAIL_COND_MSG(fae.is_null(), "Can't open encrypted pack-referenced file '" + String(pf.pack) + "'.");
		Vector<uint8_t> key;
		key.resize(32);
		for (int i = 0; i < key.size(); i++) {
			key.write[i] = script_encryption_key[i];
		}
		Error err = fae->open_and_parse(f, key, FileAccessEncrypted::MODE_READ, false);
		ERR_FAIL_COND_MSG(err, "Can't open encrypted pack-referenced file '" + String(pf.pack) + "'.");
		f = fae;
		off = 0;
	}
	pos = 0;
	eof = false;
}
Error DirAccessPack::list_dir_begin() {