PHP: Make the filter_input() function work.

On GitHub, @jamesRUS52 reported that the PHP filter_input()[0] function
would just return NULL.

To enable this function we need to run the variables through the
sapi_module.input_filter() function when we call
php_register_variable_safe().

In PHP versions prior to 7.0.0, input_filter() takes 'len' as an
unsigned int, while later versions take it as a size_t.

Now, with this commit and the following PHP

  <?php

  var_dump(filter_input(INPUT_SERVER, 'REMOTE_ADDR'));
  var_dump(filter_input(INPUT_SERVER, 'REQUEST_URI'));
  var_dump(filter_input(INPUT_GET, 'get', FILTER_SANITIZE_SPECIAL_CHARS));

  ?>

you get

  $ curl 'http://localhost:8080/854.php?get=foo<>'
  string(3) "::1"
  string(18) "/854.php?get=foo<>"
  string(13) "foo&#60;&#62;"

[0]: <https://www.php.net/manual/en/function.filter-input.php>

Tested-by: <https://github.com/jamesRUS52>
Closes: <https://github.com/nginx/unit/issues/854>
Reviewed-by: Alejandro Colomar <alx@nginx.com>
Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

src/nxt_php_sapi.c

@@ -1532,14 +1532,23 @@ static void
 nxt_php_set_sptr(nxt_unit_request_info_t *req, const char *name,
     nxt_unit_sptr_t *v, uint32_t len, zval *track_vars_array TSRMLS_DC)
 {
-    char  *str;
+    char          *str;
+#if NXT_PHP7
+    size_t        new_len;
+#else
+    unsigned int  new_len;
+#endif
 
     str = nxt_unit_sptr_get(v);
 
     nxt_unit_req_debug(req, "php: register %s='%.*s'", name, (int) len, str);
 
-    php_register_variable_safe((char *) name, str, len,
-                               track_vars_array TSRMLS_CC);
+    if (sapi_module.input_filter(PARSE_SERVER, (char *) name, &str, len,
+                                 &new_len TSRMLS_CC))
+    {
+        php_register_variable_safe((char *) name, str, new_len,
+                                   track_vars_array TSRMLS_CC);
+    }
 }