Description:
------------
Since the argument origts to 0, the null pointer is interpreted.

Test script:
---------------
<?php

class aaa extends DatePeriod {
   
	public function __construct() { }
}

$start=new DateTime( '2012-08-01' );

foreach (new aaa($start) as $y){

 $a=$key;

}


Expected result:
----------------
no crash

Actual result:
--------------
root@ubuntu:/home/hjy/Desktop# ./php-7.1.7/sapi/cli/php poc.php 
ASAN:SIGSEGV
=================================================================
==6186==ERROR: AddressSanitizer: SEGV on unknown address 0x00000000 (pc 0x081c3fb7 sp 0xbfde97f0 bp 0xbfde9818 T0)
    #0 0x81c3fb6 in memcpy /usr/include/i386-linux-gnu/bits/string3.h:51
    #1 0x81c3fb6 in timelib_time_clone /home/hjy/Desktop/php-7.1.7/ext/date/lib/timelib.c:58
    #2 0x80be985 in date_period_it_rewind /home/hjy/Desktop/php-7.1.7/ext/date/php_date.c:1947
    #3 0xa12536a in ZEND_FE_RESET_R_SPEC_VAR_HANDLER /home/hjy/Desktop/php-7.1.7/Zend/zend_vm_execute.h:16525
    #4 0x9f38f6f in execute_ex /home/hjy/Desktop/php-7.1.7/Zend/zend_vm_execute.h:429
    #5 0xa34f88b in zend_execute /home/hjy/Desktop/php-7.1.7/Zend/zend_vm_execute.h:474
    #6 0x9c69108 in zend_execute_scripts /home/hjy/Desktop/php-7.1.7/Zend/zend.c:1476
    #7 0x98eb275 in php_execute_script /home/hjy/Desktop/php-7.1.7/main/main.c:2537
    #8 0xa35f295 in do_cli /home/hjy/Desktop/php-7.1.7/sapi/cli/php_cli.c:993
    #9 0x80a8ceb in main /home/hjy/Desktop/php-7.1.7/sapi/cli/php_cli.c:1381
    #10 0xb6bdca82 in __libc_start_main (/lib/i386-linux-gnu/libc.so.6+0x19a82)
    #11 0x80a995f (/home/hjy/Desktop/php-7.1.7/sapi/cli/php+0x80a995f)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV /usr/include/i386-linux-gnu/bits/string3.h:51 memcpy
==6186==ABORTING