Missing exit out of permission check in haveged could lead to root exploit

In `src/havegecmd.c`, the `socket_handler` function performs a credential check on the abstract UNIX socket (`\0/sys/entropy/haveged`). However, while it detects if the connecting user is not root (`cred.uid != 0`) and prepares a negative acknowledgement (`ASCII_NAK`), it **fails to stop execution**. The code proceeds to the `switch` statement, allowing any local unprivileged user to execute privileged commands such as `MAGIC_CHROOT`.