conn: fix panic when remote endpoint is not set
conn: fix panic when remote endpoint is not set

If a client connects without a remote endpoint set, and a timeout
happens, the server paniced.

Fixes vanadium/issues#1132.

Change-Id: Ie0729a237380813720c20712d43457c62d170578

vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref