Check return value of dst_key_getbool()
Fix Coverity CHECKED_RETURN reports for dst_key_getbool(). In most cases we do not really care about its return value, but it is prudent to check it.
In one case, where a dst_key_getbool() error should be treated identically as success, cast the return value to void and add a relevant comment.
(cherry picked from commit e645d2ef)
Closes #2006 (closed)