Zile pegs CPU when taking stdin

[BTD Master]

Hey there,

I am trying to use zile within a shell pipeline, but doing so leaves it
in a loop:

```
rt_sigaction(SIGTSTP, {sa_handler=SIG_IGN, sa_mask=[],
sa_flags=SA_RESTORER|SA_RESTART, sa_restorer=0x7f726f91b870},
{sa_handler=0x7f726fd75d10, sa_ma> poll([{fd=0, events=POLLIN}], 1, 0)
   = 1 ([{fd=0, revents=POLLHUP}]) rt_sigaction(SIGTSTP,
{sa_handler=0x7f726fd75d10, sa_mask=[],
sa_flags=SA_RESTORER|SA_RESTART, sa_restorer=0x7f726f91b870}, NULL, 8)
= 0 read(0, "", 1)                          = 0 rt_sigaction(SIGTSTP,
{sa_handler=SIG_IGN, sa_mask=[], sa_flags=SA_RESTORER|SA_RESTART,
sa_restorer=0x7f726f91b870}, {sa_handler=0x7f726fd75d10, sa_ma>
poll([{fd=0, events=POLLIN}], 1, 0)     = 1 ([{fd=0, revents=POLLHUP}])
rt_sigaction(SIGTSTP, {sa_handler=0x7f726fd75d10, sa_mask=[],
sa_flags=SA_RESTORER|SA_RESTART, sa_restorer=0x7f726f91b870}, NULL, 8)
= 0 read(0, "", 1)                          = 0 rt_sigaction(SIGTSTP,
{sa_handler=SIG_IGN, sa_mask=[], sa_flags=SA_RESTORER|SA_RESTART,
sa_restorer=0x7f726f91b870}, {sa_handler=0x7f726fd75d10, sa_ma>
poll([{fd=0, events=POLLIN}], 1, 0)     = 1 ([{fd=0, revents=POLLHUP}])
rt_sigaction(SIGTSTP, {sa_handler=0x7f726fd75d10, sa_mask=[],
sa_flags=SA_RESTORER|SA_RESTART, sa_restorer=0x7f726f91b870}, NULL, 8)
= 0 read(0, "", 1)                          = 0 rt_sigaction(SIGTSTP,
{sa_handler=SIG_IGN, sa_mask=[], sa_flags=SA_RESTORER|SA_RESTART,
sa_restorer=0x7f726f91b870}, {sa_handler=0x7f726fd75d10, sa_ma>
poll([{fd=0, events=POLLIN}], 1, 0)     = 1 ([{fd=0, revents=POLLHUP}])
```

To reproduce (warning: bashims):
`echo Hello | zile -`
`echo Hello | strace zile - |& head -1000 | tail > log`

Thank you!