Remove unneded NULL-checking

Remove unneded NULL-checking

Fix an issue reported by Coverity by removing the unneded check.

    *** CID 352554:  Null pointer dereferences  (REVERSE_INULL)
    /bin/dig/dighost.c: 3056 in start_tcp()
    3050
    3051     	if (ISC_LINK_LINKED(query, link)) {
    3052     		next = ISC_LIST_NEXT(query, link);
    3053     	} else {
    3054     		next = NULL;
    3055     	}
    >>>    CID 352554:  Null pointer dereferences  (REVERSE_INULL)
    >>>    Null-checking "connectquery" suggests that it may be null, but it
           has already been dereferenced on all paths leading to the check.
    3056     	if (connectquery != NULL) {
    3057     		query_detach(&connectquery);
    3058     	}
    3059     	query_detach(&query);
    3060     	if (next == NULL) {
    3061     		clear_current_lookup();