Closes GH-5746

Looking at the history of this function, the original implementation had a bug where
it would return from the middle of the function without unlocking the mutex first.
The author attempted to fix this by incrementing the `initialized` flag atomically,
which is not necessary, since the section which modifies the flag is protected by a
mutex.

Coincidentally, at the same time that all this unnecessary 'atomic' machinery was
introduced, the code was also changed so that it didn't return without unlocking the
mutex. So it looks like the bug was fixed by accident.

It's not necessary to declare the flag as `volatile` either, since it is protected
by a mutex.

Further, the 'fixed' implementation was also wrong in another respect: on Windows
and Solaris, the `initialized` flag was not even declared as `static`!! So the
initialization of the static tables for S-boxes, P-boxes, etc. was repeated on
each call to `php_crypt`, completely defeating the purpose of this function.

* PHP-7.4:
  Fix #55857: ftp_size on large files

* PHP-7.3:
  Fix #55857: ftp_size on large files

`atol()` returns a `long` which is not the same as `zend_long` on
LLP64; we use `ZEND_ATOL()` instead.

There is no need for a new test case, since filesize_large.phpt already
tests for that behavior; unfortunately, the FTP test suite relies on
`pcntl_fork()` and therefore cannot be run on Windows.