Handle read errors in Protocols.LysKOM.Raw.

If there is a network outage, con->read() will return 0 (not the empty
string) after a (long) while.  Treat that properly by calling
connection_lost() in that case as well.

Fixed a backrace in conwrite by returning 0 if the connection
is closed.

(cherry picked from commit 7cdea47d)

lib/modules/Protocols.pmod/LysKOM.pmod/Raw.pike

@@ -53,6 +53,7 @@ protected inline int conwrite(string what)
 #ifdef LYSKOM_DEBUG
    werror("-> %O\n",what);
 #endif
+   if (!con) return 0;
    int i=con->write(what)==sizeof(what);
    if (!i) { werror("write failed!!!\n"); _exit(1); }
    return i;
@@ -282,6 +283,7 @@ void read_thread()
       }
       recv(0,s);
    }
+   connection_lost();
 }
 
 #if constant(thread_create) && !LYSKOM_UNTHREADED