Description:
------------
very similar to Bug #41518 [https://bugs.php.net/bug.php?id=41518], but happening in a much narrower case.
consider following file structure exists:
- parent
 - folder1
  - image2.jpg
 - file.txt

with open_basedir enabled, consider one tries to perform file_exists($filename) with $filename within the permitted paths. three cases are presented:

- $filename = 'path/to/parent/folder1/image.jpg'
    file does not exists but the containing folder (folder1) does. file_exists() returns false as expected.

- $filename = 'path/to/parent/folder2/image.jpg'
    neither file nor it's containing folder (folder2) do not exist. file_exists() returns false as expected.

- $filename = 'path/to/parent/file.txt/image.jpg'
    the target file (image.jpg) does not exist but there is a file named file.txt, in this case when file_exists() tries to look into file.txt (it assumes it's a folder) an open_basedir restriction warning arises. file_exists() still returns false.

same thing happens with is_file and is_dir functions.
I've checked it on PHP 5.6.30 and 7.0.12 and same thing happens on both versions.


Test script:
---------------
ini_set('open_basedir', 'path/to/parent');

file_exists('path/to/parent/folder1/image.jpg'); // returns false
file_exists('path/to/parent/folder2/image.jpg'); // returns false
file_exists('path/to/parent/file.txt/image.jpg'); // returns false and causes open_basedir warning 

Expected result:
----------------
all three cases should return false without warning. as the given $filename to file_exists() function is located under allowed paths.

Actual result:
--------------
the third function call results in following warning:
Warning: file_exists(): open_basedir restriction in effect.