Description:
------------
strftime returns empty string when input fmt string exceeds 1024

due to the undocumented code logic in 'ext/date/php_date.c' php_strftime
...
    int                  max_reallocs = 5;
    size_t               buf_len = 256, real_len;
...
    buf = (char *) emalloc(buf_len);
    while ((real_len=strftime(buf, buf_len, format, &ta))==buf_len || real_len==0) {
        buf_len *= 2;
        buf = (char *) erealloc(buf, buf_len);
        if (!--max_reallocs) {
            break;
        }
    }  
...

the logic to abort reallocation after 5 times is undocumented.
thus we can have at most 256 * 5 = 1024 size string.

Test script:
---------------
echo strftime(str_repeat('x', 1024));

Expected result:
----------------
should output 1024 occurrences of 'x' 

Actual result:
--------------
empty string