[2019-12-28] - Found with Honggfuzz

NULL pointer dereference in the S_pending_ident() function, in toke.c.

Issue can be reproduced by running:

```
perl test01.pl
```

```
AddressSanitizer:DEADLYSIGNAL
=================================================================
==13609==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000008 (pc 0x0000005857d1 bp 0x7ffd300e8150 sp 0x7ffd300e6f80 T0)
==13609==The signal is caused by a READ memory access.
==13609==Hint: address points to the zero page.
    #0 0x5857d0 in S_pending_ident /home/fcambus/perl-5.30.1/toke.c:9111:17
    #1 0x5857d0 in Perl_yylex /home/fcambus/perl-5.30.1/toke.c:4903:13
    #2 0x5d21cc in Perl_yyparse /home/fcambus/perl-5.30.1/perly.c:340:34
    #3 0x54cfa0 in S_parse_body /home/fcambus/perl-5.30.1/perl.c:2531:9
    #4 0x54cfa0 in perl_parse /home/fcambus/perl-5.30.1/perl.c:1822:2
    #5 0x4df38c in main /home/fcambus/perl-5.30.1/perlmain.c:126:10
    #6 0x7f1b520c11e2 in __libc_start_main /build/glibc-4WA41p/glibc-2.30/csu/../csu/libc-start.c:308:16
    #7 0x437bfd in _start (/home/fcambus/perl-5.30.1/perl+0x437bfd)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV /home/fcambus/perl-5.30.1/toke.c:9111:17 in S_pending_ident
==13609==ABORTING
```