libadmin: appease clang -Wsometimes-uninitialized

libadmin: appease clang -Wsometimes-uninitialized

clang thinks that 'time' can be used uninitialized:

bos.c:1472:9: error: variable 'time' is used uninitialized whenever 'if' condition is
      false [-Werror,-Wsometimes-uninitialized]
    if (as->parms[TIME].items) {
        ^~~~~~~~~~~~~~~~~~~~~
bos.c:1478:57: note: uninitialized use occurs here
    if (!bos_ExecutableRestartTimeSet(bos_server, type, time, &st)) {
                                                        ^~~~
bos.c:1472:5: note: remove the 'if' if its condition is always true
    if (as->parms[TIME].items) {
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~
bos.c:1445:5: note: variable 'time' is declared here
    bos_RestartTime_t time;
    ^

but in this command description, the TIME argument is required.
Add a never-triggered error exit to appease the compiler when
--enable-checking is activated.

Change-Id: I38fac64fc5aba071f84f2f9e1b497df22df76f09
Reviewed-on: https://gerrit.openafs.org/13476
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Cheyenne Wills <cwills@sinenomine.net>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>