console: fix -i being overruled by !isatty()

The interactive mode has been ignored when stdin was not a tty and is no
more. Now results of another command can be handled by tarantool.
Before the patch:
```
$ echo 42 | tarantool -i
LuajitError: stdin:1: unexpected symbol near '42'
fatal error, exiting the event loop
```

After the patch:
```
$ echo 42 | tarantool -i
Tarantool 2.5.0-130-ge3cf64a6c
type 'help' for interactive help
tarantool> 42
---
- 42
...

```

Closes #5064

NO_DOC=bugfix

(cherry picked from commit 9965e3fe)