We always has a valid `line` when we reach here.  Actually combined with above comments, we can have:
```
RIL_SignalStrength_v6 response;
line = p = strdup(s);
if (!line) {
    ALOGE("+CSQ: Unable to allocate memory");
    return;
}
if (at_tok_start(&p) < 0) {
    ALOGE("invalid +CSQ response: %s", s);
    goto error;
}
if (handleSignalStrength(p, &response) < 0) {
    goto error;
}
RIL_onUnsolicitedResponse(RIL_UNSOL_SIGNAL_STRENGTH, &response, sizeof response);

error:
free(line);
return;
```