Fix static members null pointer exception

[vtsykun]

Fixes: #129

STR:

1. create classes

if (\PHP_VERSION_ID >= 80000) {
    class TokenPolyfill extends \PhpToken {
    }
    return;
}

class TokenPolyfill {
private static array $identifierTokens;
}

2. Create object

$req = new TokenPolyfill(\T_NULLSAFE_OBJECT_OPERATOR, '?->', 10, 10);
\meminfo_dump(\fopen('/tmp/mem_dump.json', 'w'));

3. Segmentation fault

Program received signal SIGSEGV, Segmentation fault
0x00007ffff2b43fb6 in meminfo_browse_class_static_members (stream=stream@entry=0x7ffff54c2ee0, visited_items=visited_items@entry=0x7fffed5f8cf0, first_element=first_element@entry=0x7fffed5f8ce4)
    at /opt/progs/php-meminfo/extension/meminfo.c:147
147	        if (class_entry->default_static_members_count > 0 && CE_STATIC_MEMBERS(class_entry)) {
(gdb) bt 
#0  0x00007ffff2b43fb6 in meminfo_browse_class_static_members (stream=stream@entry=0x7ffff54c2ee0, visited_items=visited_items@entry=0x7fffed5f8cf0, first_element=first_element@entry=0x7fffed5f8ce4)
    at /opt/progs/php-meminfo/extension/meminfo.c:147
#1  0x00007ffff2b445be in zif_meminfo_dump (execute_data=<optimized out>, return_value=<optimized out>) at /opt/progs/php-meminfo/extension/meminfo.c:80
#2  0x00005555558a5d48 in execute_ex ()
#3  0x000055555582dcbc in zend_call_function ()
#4  0x00005555558d72c9 in ?? ()
#5  0x00005555558d82b2 in ?? ()
#6  0x00005555557d6287 in make_fcontext ()
#7  0x0000000000000000 in ?? ()