Issue

• Tab completion after a subshell command causes ZSH to crash:

$ zsh
$ autoload -U compinit && compinit -u
$ echo $(echo x)<TAB>
zsh: fatal error: out of memory

• GDB Backtrace:

#0  __GI_exit (status=1) at exit.c:99
#1  0x0000000000453181 in zalloc ()
#2  0x00007ffff0309a54 in do_completion () from /usr/lib64/zsh/5.0.2/zsh/complete.so
#3  0x00007ffff054c3ef in docomplete () from /usr/lib64/zsh/5.0.2/zsh/zle.so
#4  0x00007ffff0548d10 in completecall () from /usr/lib64/zsh/5.0.2/zsh/zle.so
#5  0x00007ffff053a2b6 in execzlefunc () from /usr/lib64/zsh/5.0.2/zsh/zle.so
#6  0x00007ffff053a5b9 in zlecore () from /usr/lib64/zsh/5.0.2/zsh/zle.so
#7  0x00007ffff053b1dd in zleread () from /usr/lib64/zsh/5.0.2/zsh/zle.so
#8  0x00000000004405d2 in zleentry ()
#9  0x00000000004419d6 in ingetc ()
#10 0x000000000043abf6 in ihgetc ()
#11 0x000000000044b91e in zshlex ()
#12 0x0000000000469036 in parse_event ()
#13 0x000000000043dc3e in loop ()
#14 0x0000000000440fce in zsh_main ()
#15 0x00007ffff6ecab15 in __libc_start_main (main=0x40ed00 <main>, argc=1, ubp_av=0x7fffffffdb08, init=<optimized out>, fini=<optimized out>, 
    rtld_fini=<optimized out>, stack_end=0x7fffffffdaf8) at libc-start.c:274
#16 0x000000000040ed31 in _start ()