openFile: Fail correctly if the file doesn't exist

[Naktibalda]

I fixed 2 issues:

 I see file found "_log/.gitkeep"
<warning>PHP Warning:  file_get_contents(/.../Codeception/tests/data/included/tests/data/included/_log/.gitkeep): Failed to open stream: No such file or directory in /.../Codeception/vendor/codeception/module-filesystem/src/Codeception/Module/Filesystem.php on line 78</warning>
TypeError: Cannot assign bool to property Codeception\Module\Filesystem::$file of type string

 I am in path "tests/data/included"
<warning>PHP Warning:  chdir(): No such file or directory (errno 2) in /.../Codeception/vendor/codeception/module-filesystem/src/Codeception/Module/Filesystem.php on line 46</warning>
  Moved to /.../Codeception/tests/data/included