dont export/unset if they are piped

[Han2-Ro]

use the same logic as in exit

[Han2-Ro]

bash behaviour: export with args, unset, exit seem to do nothing if they are piped. But they do stuff like normal with redirect into a file

current minishell behavior: exit does nothing if redirected (pipe or file) export unset always do what they do

[aprevrah]

resolved by #146