[perl #125351] null ptr deref -> Perl_ck_shift (op.c:10857)

From v5.25.4 (v5.25.3-305-g8c6b0c7):

./perl -e 'qq{@{sub{q}}]]}};s0{shift'

ASAN:SIGSEGV
=================================================================
==31752==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x00000055ff13 bp 0x7ffda0f99310 sp 0x7ffda0f99110 T0)
    #0 0x55ff12 in Perl_ck_shift /root/perl/op.c:10881:7
    #1 0x6b5f8c in Perl_yyparse /root/perl/perly.y:1166:23
    #2 0x59c4a1 in S_parse_body /root/perl/perl.c:2372:9
    #3 0x59283c in perl_parse /root/perl/perl.c:1688:2
    #4 0x4de835 in main /root/perl/perlmain.c:121:18
    #5 0x7f34f1834b44 in __libc_start_main /build/glibc-uPj9cH/glibc-2.19/csu/libc-start.c:287
    #6 0x4de4cc in _start (/root/perl/perl+0x4de4cc)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV /root/perl/op.c:10881 Perl_ck_shift
==31752==ABORTING

• [perl #125351] null ptr deref -> Perl_ck_shift (op.c:10857) by Brian Carpenter via RT