Upstream was a little premature on asking for a change and not
vetting it.  Here is the currently proposed fix.

Signed-off-by: Philip Prindeville <philipp@redfish-solutions.com>

Depending on which version of libiconv you're using, php_iconv_string()
doesn't always null out *out as part of its initialization.  This
patch makes that behavior invariant.

Submitted upstream as https://github.com/php/php-src/pull/3037 where
it's approved and waiting a merge.

Signed-off-by: Philip Prindeville <philipp@redfish-solutions.com>