bug#55344: ftw thinks readable directories are unreadable if "other" don't have read permission

ftw incorrectly thinks that if other users don't have the read 
permission then the owner can't read it either. This also affects ntfw.

Guile version: 3.0.8
Machine type: x86_64-pc-linux-gnu
[email protected] from Guix

To reproduce: Create 2 directories, one with rwxrwxrwx permissions and 
another with rwxrwx---. Then pass them to ftw and notice it won't 
recurse because it thinks they're directory-not-readable.

scheme@(guile-user)> (passwd:uid (getpw (getlogin)))
$1 = 1001
scheme@(guile-user)> (stat:uid (stat "readable-dir"))
$2 = 1001
scheme@(guile-user)> (stat:uid (stat "also-readable-dir"))
$3 = 1001
scheme@(guile-user)> (format #f "~o" (stat:perms (stat "readable-dir")))
$4 = "777"
scheme@(guile-user)> (format #f "~o" (stat:perms (stat 
"also-readable-dir")))
$5 = "770"
scheme@(guile-user)> (stat "readable-dir")
$6 = #(24 61374845 16895 1 1001 998 0 0 1652140343 1652140343 1652141421 
4096 0 directory 511 216530924 216530924 1652141421)
scheme@(guile-user)> (stat "also-readable-dir")
$7 = #(24 61374847 16888 1 1001 998 0 0 1652140345 1652140345 1652141426 
4096 0 directory 504 20542871 20542871 1652141426)
scheme@(guile-user)> (ftw "readable-dir" (lambda (filename statinfo 
flag) (display flag) (newline) #t))
directory
$8 = #t
scheme@(guile-user)> (ftw "also-readable-dir" (lambda (filename statinfo 
flag) (display flag) (newline) #t))directory-not-readable
$9 = #t