`tr`: exit with no error when pipe broken

GNU coreutils:
```console
$ tr -dc '[:alnum:]' </dev/urandom | head -c 25
jN1qGXaE0GNVEnIRMPDuBViEd
```
uutils coreutils:
```console
$ tr -dc '[:alnum:]' </dev/urandom | head -c 25
CRJV9SipwMwDLp6TOvi45mh5Etr: write error: Broken pipe
```